Circuit overload, ground fault, and short circuit are the three basic causes for your circuit breaker to trip, all of which are surprisingly frequent.
It's a good idea to hire a professional electrician if your circuit breaker keeps tripping. Short circuits and ground faults may be detected and safely repaired by an electrician. He or she will also be the best person to service your electrical panel and replace any breakers that are undersized, broken, old, or otherwise on the verge of failing.