you might want to look up behavioral finance, which studies behavior in financial markets by focusing on psychological factors that influence decision-making during uncertainty. Many top programs offer courses in such area. (eg Chicago GSB, Yale SOM). Bear in mind, however, that there are just courses you may take to supplement your interest in psychology.
remember that behavioral finance is a subdiscipline of finance. MBA is a professional degree, so at best, I guess you'll probably end up taking just a class or two because of your interest in psychology.
Another area you might find interesting is organizational behavior. I don't know anything about possible career path. Many top MBA programs offer such courses, so do some PhD programs