Happens when you use the computer/internet too much.
Are you a gamer/nerd? Try limiting your time on the computer, go spend some time outdoors and just hanging out with your friends. The problem is you think they expect something from you, when they really don't. They just want to be your friend and have someone to talk to - even if you aren't that smart and are nervous of saying something stupid, that's fine just realize no one is perfect.
I think I was like this too when I was younger. I played Runescape all day and felt nervous when talking to people cuz of those awkward silences where I didn't know what to say. After a few years of college and a better education, small talk comes more easily. Also, make sure you stay up to date with news and shit and you will have plenty to talk about. You just gotta get involved with something and do your best to enjoy it.