Are you using a laptop? If so, you could be bumping the touchpad, so all you would have to do is disable it in the control panel(Mouse settings). If you are using a desktop, it might be the surface your using it on, tr using a mouse pad or if you have another mouse, plug it in and see if you get the same problem.
Let me know how you get on.
Good luck :-)
Spartica
September 2009