Does streaming music over Bluetooth in car charge data fees?

If I have an unlimited data plan on my iphone will it eventually charge me more using Bluetooth? I'm so out of the loop.

If you have unlimited data then you have nothing to worry about. If you had limited data, then streaming data over your carrier's data network (internet) is what would count toward your data allowance. Bluetooth is just a local wireless connection between your phone and you car, so that would not count. However, if you are streaming audio from an internet music service then that would use your carrier's data.