I don't think its anything to do with your keyboard.
Computers do chuck out a load of RF (radio frequency) noise when they are in use, so that is what is being picked up.
Try and make sure all the signal wires are as far away from each other as possible, particularly the telephone wire if you are using ADSL and the coaxial cable.
Check to make sure all the coaxial plug sleeves are not loose, if they are tighten them.
If the problem persists you'll have to try a process of elimination, try plugging the antenna cable straight into the TV so the digibox is bypassed, if the cures it the problem is with the digibox. I fact you try this first to see where the problem is,