New Leak in water heater

I just woke up to a small leak in my water heater. It is a gas heater. The leak is like a faucet drip (slow). It comes from the rear of the tank. The heater is about 5 years old, and has never done this before. Does this mean I remove and replace the heater, or will a repair be in order. I dont know if I can find my way back here, so an answer to [email protected] would be a great help. Thanks in advance.