If you are referring to a game where your opponent had a king + lone bishop, and you had a king + 3 pawns, then yes, you lost the game.
It is correct in FIDE, article 6.9. :
http://www.fide.com/component/handbook/?id=124&view=article
the mate is possible, note that it doesn't have to be probable.
Today I played and I had trouble with clock so at the end I tried to capture all the pawns so my opponent will have only a bishop, which I thought wouldn't be sufficient to win. So I captured the last pawn and my opponent captured my rook leaving my opponent with only king and bishop, but he won on time. Is this correct (FIDE rule)?