Is rook and bishop vs. rook and pawn a draw?

I give you high marks for the brevity of your question, but there are times when details can be quite useful. If the pawn is on the seventh rank and about to queen, the "weaker" side could be winning. I'll assume you mean a position where no pieces are about to be lost by tactics and the pawn is protected but not dangerous. In such a case the pawn can usually be won and the weaker side will have to defend rook and bishop v. rook. That ending generally starts out as a "theoretical draw" with perfect play, though I would say that the stronger side reaches a winning position in a majority of games. The king is usually driven to the side of the board and careful play (or encyclopedic knowledge) is required to avoid checkmate or loss of the rook.