If the water is coming from the relief valve, one of the elements is probably bad. Sometimes elements can continue to heat, even after the heater has reached the set temperature, when the elements have corroded.
If the water is not coming from the relief valve, ensure the water is not coming from a plumbing connection to the heater. If the plumbing connections are dry, the tank is leaking, and you will need to replace the unit.
If the water is not coming from the relief valve, ensure the water is not coming from a plumbing connection to the heater. If the plumbing connections are dry, the tank is leaking, and you will need to replace the unit.