Most people become extremely nervous at the prospect of a job interview.
Some nervousness is to be expected. However you can cut down on your worry about an interview by recognizing it as a conversation between you and a potential employer designed to give both of you the information necessary to determine if you want the position and if they want to hire you. The other key to interviewing successfully and with a minimum of anxiety is preparation. The better prepared you are the more confident you will be. You need to know if you want to work there.