A wet circuit breaker can be a very dangerous and serious issue. You should call your trusted licensed Mister Sparky electrician to further investigate safely. The moisture will eventually dissipate. Do not touch any electrical wiring system that is energized that may be wet. Look for signs of smoke as a wet circuit breaker is not only a shock hazard, but a fire hazard as well. Also, it is important to make sure you are not standing in water while working with any components of the circuit breaker.
Check the Circuit Breaker
You might want to search for the reason water is entering your circuit breaker. This could be because of heavy rain or even a leak near your breaker panel. If there is a leak, you will want to address and correct that issue immediately. If water has entered because of rain, you might want to double check the sealing.
There are ways to help prevent water from entering your panel. They make weatherproof panels, meters and boxes that are designed to release the water if it does mange to enter your breaker box.