Sorry to hear you are having a problem with your Comcast remote control. I would like to suggest a few things before having you exchange the remote control.
First, try changing the batteries in the remote control.
Another thing to try would be to unplug your cable box from the AC power outlet and then plug it back in again. That may straighten things out.
Sometimes there can also be interference with compact florescent light bulbs (CFLs) in the room.
If you are still having a problem, you can exchange your Comcast remote control at any of our area service centers at no charge or call us at 1-800-COMCAST and we can arrange to get a replacement remote control out to you.