To stop your cat from walking across your computer keyboard, you may be able to use the same methods that can be successful at keeping cats off of the counter . This works fine if we are waiting for him, but not when we aren't in the room.
Balloons can be a festive deterrent.
Blow up a balloon and let your cat sniff it, then pop it by the side of his head. If this is done several times, the cat will soon start to detest balloons, at which time you can place the balloons around your keyboard. This may convince your cat to leave the keyboard alone. There are several devices available commercially which may be helpful. Large plastic devices which look like mousetraps can be placed on the desk near the keyboard, and when the cat jumps on them, the paddle will slap making a loud scary noise.