Property management is a business that is regulated and requires a real estate license, as well as a business license in most states. Check with your local City Hall for the Business license and regulations.
If you are performing real estate services for a fee, you need a real estate brokerage license first. The fact that you asked if you need a general business license tells me you likely don't have a brokers license as of yet. I am from Florida where it is a 3rd degree felony to practice real estate without a license, I'm sure its still criminal in California.