I was like this with my first boss. Some of this can be tied to lack of experience in the workplace. It also doesn't help if the manager in question is one who doesn't give feedback easily. So you really don't know what he thinks of you.
Now I don't know if you are new in the workplace or not. But if you are, I think you will find that this anxiety will reduce over time as you become more confident professionally. Remember, they are people too. Some are good people, some are not, just like all the rest of your co-workers.
Most bosses though want their employees to succeed and part of their job is to help you do so. So they aren't the enemy. A good boss is one of the best resources you can have for your career. Even a bad boss can end up giving you useful experience. (One of my worst bosses couldn't make a decsion to save his own life, so as a very junior person, I ended up making alot of his decisions, it helped me immensely when I was more senior to have had that experience.)
The main thing a boss wants is for the work to go well. If you do your job and do it well, then the boss will come to rely on you and you will feel less uncomfortable as you realize he sees you as an asset not as someone to fire. Sometimes at the beginning of your career, it is hard to feel confident becasue there is so much you don't know yet. It will get better as you advance from being junior to being more senior.
However, the way you phrase the question makes me think that there is a an underlying issue beyond lack of experience in the workplace. If all authority makes you anxious all the time and it makes the workplace very stressful on a daily basis, this might be something that needs to be addressed with a mental health professional. There are some good anti-anxiety drugs that can help you be better able to deal in the workplace. The truth is, you can avoid some things that make you anxious, but it is really hard to avoid having a boss unless you own your own company. So if you think this is affecting your ability to work well, then truly go seek some help.