There is a hotkey to re-centre the screen focus, or you can click the active character portrait once, or the secondary character portrait twice. Left clicking and holding the button down (so your characters follow the cursor) will also automatically re-centre the screen focus.
There is no option to prevent the cursor from moving the screen focus, since there are several situations where the characters have to split up to do something. I've gotten use to this, and don't accidentally bump the screen focus as often when using the potion bar, etc.
Welcome to the forum. <img src="/ubbthreads/images/graemlins/wave.gif" alt="" />