I don't know why it does this. Any solutions?

Do you mean by itself or with the mouse?

By itself. I've had that happen to me before. Not sure what I did to fix it. I think it's the save file. Try loading an earlier saved game or re-saving.

Although I am sure you have fixed this by now, should it happen to anyone else, hit backspace. Usually the game is repeating entering a number from the keypad (in the case of right, 6). If that doesn't work, open up the journal (J), double click an entry, and then hit backspace. That should fix this bug.

Hope that helps!

If CJAwesome's suggestion doesn't work, what usually works for me is a combination of hitting num lock and the corresponding number on the numpad to the direction the camera is going.

I'm actually having the same problem. I've hit backspace in/out of the journal, and I've fiddled with numlock as well, neither of which seem to work. Interestingly, if I hit any of the number keys that correspond to movement, the screen will start scrolling in THAT direction instead, but only for as long as I'm holding the key down. Nothing seems to actually STOP the scrolling.

I'm also having this problem, no solutions ITT have helped

Make sure you haven't got the Scroll Lock key on.
Have you tried rebooting your computer?