Definitely not an Associate Professor, I'm afraid!

You have to be careful with academic ranks; the terminology is very country-specific. The Australian terms are similar to British, with certain differences, and quite unlike American. So "Professor" means catedrático, not profesor.

First, what is a "profesor asociado"? I presume we're talking about Spain. It's a non-tenured university teacher with notable (non-academic) professional experience, on a temporary renewable contract:

"Profesores asociados
El profesor asociado universitario proporciona a la institución educativa universidad el conocimiento y la experiencia del profesional. Según establece la Ley Orgánica 4/2007, de 12 de abril, los requisitos de acceso para este tipo de figura docente son los siguientes:
- El contrato se podrá establecer con especialistas de reconocida competencia que acrediten ejercer su actividad profesional fuera del ámbito académico universitario.
- La finalidad del mismo será la de desarrollar tareas docentes a través de las que se aporten sus conocimientos y experiencias profesionales a la universidad.
- El contrato será de carácter temporal y con dedicación a tiempo parcial. La duración del mismo será trimestral, semestral o anual, y se podrá renovar por periodos de igual duración, siempre que se siga acreditando el ejercicio de la actividad profesional fuera del ámbito académico universitario."
http://profesores.universia.es/carrera-academica/contratacio...

But an Associate Professor in Australia is the second highest tenured rank, just below Professor and above Senior Lecturer, which is quite different from a profesor asociado.
http://en.wikipedia.org/wiki/Academic_ranks_(Australia_and_N...

The nearest equivalent, I think, is an Adjunct Lecturer. The term "adjunct" is used in Australian universities for people who hold honorary teaching positions on a temporary (though renewable) basis, and it's used especially for noted professionals. Here's the description from the University of Sydney:

"8 Adjunct titles
(1) Adjunct titles may be conferred on individuals who are expert in an appropriate field and who are contributing significantly to teaching or research, or who are fostering partnerships between the University and industry, a profession or the wider community.
(2) Adjunct titles may be conferred on individuals in professional practice with the aim of facilitating the integration of the academic and professional components of academic programs.
(3) Holders of adjunct titles are not necessarily required to have an academic background.
(4) Co mmittees constituted to consider the award of adjunct titles will be guided by the following normative criteria.
(a) Adjunct Associate Lecturer: c ontribution by an employee of a public or private organisation to academic, professional, or business development.
(b) Adjunct Lecturer: leadership at a local level of a public or private organisation; contribution to academic or professional or
business development.
(c) Adjunct Senior Lecturer: leadership at state or regional level of a significant public or private organisation; independent contribution to academic, professional or business development.
(d) Adjunct Associate Professor: leadership at national level of a significant public or private organisation; significant contribution to academic, professional or business development.
(e) Adjunct Professor: leadership at national or international level of a major public or private organisation; outstanding independent contribution to academic, professional or
business development."
http://sydney.edu.au/policies/showdoc.aspx?recnum=PDOC2013/3...

Other Australian universities seems to use these titles in a similar way.

So really it corresponds quite closely to the idea of a Spanish profesor asociado. As you can see, there can be different grades of adjunct staff, in parallel with the tenured ranks. So in principle the term will depend on how eminent the person concerned is. By default I'd be inclined to use "Adjunct Lecturer" as a generic term. To be an Adjunct Professor you have to be really distinguished. But you may be able to judge from your context.

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Note added at 57 mins (2014-02-17 11:00:59 GMT)
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I forgot to say that in any case I would recommend giving this person his/her Spanish title of "Profesor asociado" and adding the Australian equivalent, "Adjunct Lecturer", in parentheses.

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Note added at 1 hr (2014-02-17 11:19:29 GMT)
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I thought about "Associate Lecturer", which is a fixed-term appointment and is non-tenured (I think), but it's normally for very junior academics, not professionals; it's the first rung on the academic ladder, from which you (hopefully) move on quite quickly to tenured Lecturer. So I don't think it's so suitable for this.