I am a computer tech and I've found that the primary cause for what you describe is that you are using a laptop computer, and while you type, your palms are inadvertently touching the laptop touch-pad. Any touch on a touch-pad tells the computer to move the "mouse" pointer. This will relocation the position you are typing text. So if you are using laptop computer, you need to lift your palms. An alternative is to disable the touch-pad. There is a setting in Windows to disable the touch-pad if a computer mouse is attached. Ask for these instructions if you want them. If you are not using a laptop computer, then perhaps your computer mouse is malfunctioning. It can be as simple as having the mouse on a dirty surface, or a bad mouse. First clean the mouse and the surface it is on.