My keyboard is randomly typing wrong letters

Hello,
my keyboard gradually start to randomly type wrong letters. But its not that a certain key types one other letter, the same key if pressed repeatedly will continue to type different letters - at first just a few letters will type wrong, and gradually to the point that the entire key board just types different letters / numbers / symbols at random. when I restart the computer the keyboard restores and types correctly until some times later when this starts again. what is going on? is that a virus? I ran my antivirus softwear and did not find anything.
thanks for your suggestions.
keren.