If you are referring to Propecia, then the answer is no. It has no anti-progesterone effects that I am aware of. It in technically an inhibitor of 5-alpha reductase, which means that it helps prevent the conversion of testosterone into DHT. If you do some poking around on the hair loss boards, you'll find many non AAS users who claim that Propecia alone can cause gyno. I have no idea through what mechanism, if any.
Poly