No, a circuit breaker is not a lockout device. It is an electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. During LOTO procedures, it is locked out using a circuit breaker lockout to ensure it does not automatically turn on.
By definition, a lockout device is any device that can isolate energy sources so that a piece of equipment is de-energized. This is a safety mechanism for reducing electrical hazards in the workplace.