Toshiba Satellite keyboard malfunction

My 1 year old Toshiba Satellite M645-S4114 laptop's keyboard has begun to malfunction erratically. Several times a day *any* key one types displays a number--not just keys in the area that are toggled by the numlock function key. When this happens, you cannot make the keyboard type letters--only the mouse works as expected. I've tried various function keys to no avail The only way I've found to revert back to a normal keyboard is to log off and back on again (or reboot). Any thoughts on what might be causing this problem?