If you mean "The computer records whatever it's playing to the speakers even if I turn those off", then you need to make sure that the audio software and/or drivers (via control panel) are set to record from Mic only and not "Stereo Mix" or anything else.
If you mean "The mic picks up sound coming from the speakers", then thats nothing to do with the computer/software/drivers of course. Use headphones like wot they do in recording studios.
