I often have the same problem, however I've discovered that it is do to my laptop touch pad. When I'm type I'll accidently hit the keypad causing the mouse to click, changing the place of my curser. Anyoing, yes, but easly solved. You can try one of two solutions. One: adjust the sensitivity of your touch pad so that a simple tap won's cause a problem or Two: move you mouse to an area of the page blow the text you are typing so that when it clicks, your curser stays in the same place.
Hope that helps.