Of course. If the batsman is out of his ground (i.e he has no part of his foot or bat behind the batting crease), is not attempting a run and the keeper breaks the stumps at the striker's end, he is out stumped. It does not matter if the keeper throws underarm, overarm or simply hits the wicket with the ball in his glove - the result is the same. However it is highly unlikely the batsman will be far enough out of his ground for the wicket keeper to thrown down the stumps particularly with an over arm throw. In summary, the reply is 'yes, but it's unlikely'. The previous answers differentiating between 'stumped' and 'run out' are misleading.
Further to all people saying it would be 'run out', then NOT NECESSARILY!!! The definition of a stumping is:
In cricket, a batsman can be out stumped if:
the wicket-keeper puts down the wicket, while
the batsman is:
out of his ground (because he has moved down the pitch beyond the popping crease, usually in an attempt to hit the ball),
receiving a delivery which is not a no ball, and
not attempting a run.
YOU HAVE TO BE ATTEMPTING A RUN TO BE RUN OUT!!!! Therefore a batsman CAN be out stumped and NOT run out from an overarm throw by the wicketkeeper if he is not attempting a run. End of chat.