Stiff voice happens when your voice sounds like it is not moving the way it should. It might sound like you are talking in a robot voice or like you have a very sore throat. This can happen if the muscles in your throat and voice box are not relaxed like they should be. Sometimes this happens when you get nervous or scared, and other times it can be caused by medical problems. Your doctor can help figure out why your voice might be stiff and give you ways to help make it feel better.