Depends on how sore they are. If it's just a little residual soreness, I'd say it's o.k. to work them again. On the other hand, if you are still very sore "after a couple of days," it could be a sign of overtraining (either intensity or frequency). I sometimes find that if my muscles have a bit of residual soreness in them, it goes away once I begin to work out (this happened when I did an especially intense arm workout--can't remember which one :-().