If you are using a desktop with a keyboard, then you might try using a different keyboard (if available) to see if there may be an issue with your current keyboard.
Is this only happening in IE9, and not say while typing in Notepad, WordPad, etc....?
If this is only happening in IE9, then you might see if completely
resetting IE9 may help if it was a 3rd party toolbar or add-on that may have been causing this.