It's probably what didchanowat suggested... used to happen on my mum's laptop all the time, the tapping sensitivity was turned all the way up; sometimes when your palm/finger touches it, even just a tiny bit you can't even feel, it will be registered as a "tap", or a click. I would go to mouse/"pointing device" properties and either disable tapping or turn the sensitivity down. Or if you have a compaq/HP laptop, you can just disable the touchpad altogether by clicking the small button right above it.