Do you still have the issue if you use an external mouse and external keyboard?
If you don't use an external mouse:
Be careful not to touch the fingerpad when you type. Many people touch it and don't even realize they are doing it. You don't have to press hard, in some cases it will move if you just barely graze it.
There is a possibility that you may have a loose cable that connects the touchpad to motherboard OR there could be a issue with your motherboard.
There is also a small chance that you could have an annoying virus. I have read about some that are just a nucince like one that disables the "O" button but only on the nights of a full moon. This type of virus is rare and unlikely.