Concentrate on the music and everything else will take care of itself. There are a tonne of bands where people don't really move and they're hugely respected. For example, Pink Floyd, the lead singer of Lynard Skynard, Robert Fripp sits on a chair.
Live music is live not just because people jump about - it's because you're playing LIVE. That means the sound is 3D and LOUD and it's coming from amps and it's being made right there and then. If you feel somewhere deep inside that you'd like to jump about but you're too shy or whatever, then you have to force yourself to do it, because it's your desire to do it, so that's ok, you just have to get over the fear. If you don't really want to do it, and you're comfortable to play and not really move and that's just you, then don't do it. You'll only look dumb if you do something you don't want to do.
Also, the better the music gets, the more you will naturally move without even realising you're doing it.
I've seen some utterly shite bands that jump about loads - they just look like imbeciles. I've also seen really good musicians that hardly move. You're on that stage to do what you want, so you just have to be honest about what sort of impression you want to create and get over the fear, whether it's of being extravert, or being accepted as an introvert.