Are friends jealous of each other?

Yes I agree. And I also think that's part of the reason people say, "keep your friends close and your enemies closer." I think sometimes we call someone a friend, mearly to keep them close enough to compete and compare ourselves with. I say we and our, meaning the entire human race, I don't think anyone cans say they've NEVER done this, even if it isn't an everyday thing.
JMO

Between me and my bestfriend, it hasn't happened. We actually complement each other. We even worked great together because we appreciated each other's strengths.

I somehow disagree. In the relationship I have with my friends, whenever one excels than the other, we try our best to help one another, specially in academics. Yes I agree that there comes a time we tend to be jealous, but this jealousy, I think, often drives us to strive harder and excel too.