I understand your passion towards Psychology, ergonomics is one particular component in this field. Hence you need to make up your mind to choose your study, further. Since your yet studying, try to do a vivid research. Mechanical Engineering and Psychology are 2 extremes.
MBA (HR) & MA (Psychology) are two fields of study. They are slightly inter-linked. Anyways, you need not worry as there are plenty of Job opportunities.
9th April 2012 From India, Kottayam