It depends on the context. What kind of freak is he? Is he abnormal or unconventional? For example,
abnormal: a freak storm (i.e., it's not what's expected.); S/he's a freak (i.e., Her/his character or body image isn't what we expect. It doesn't fit what's considered "normal", "average". Maybe s/he has blue hair? Maybe s/he behaves in a way that's not "normal").
unconventional: a movie freak (i.e., a person who likes movies more than the average person. S/he watches a lot of movies, loves movies, and knows everything about movies)