Presumably the PC has a 'touchpad' for driving the mouse pointer around the screen, and am I right in thinking you use a standard mouse?
Sometimes the two just don't like living together, so disable the touchpad or the mouse whichever you prefer.
The problem could also be that as you type on the keyboard, your thumbs or wrists are perilously close to the surface of the touchpad, and is moving the pointer around. These touchpads sometimes don't need to be touched at all. I think it is possible to reduce the sensitivity of it.