A mobile robot includes a body, a propulsion module, an ultrasound sensor module that is configured to detect a boundary of a cleaning area using a sound wave, and a controller configured to control the propulsion module based on the determined boundary. The ultrasound sensor module may include an ultrasonic sensor unit and a boundary detector. The sensor unit may emit the sound wave, receive the reflected sound wave from a target, and output a sound wave signal. And, the boundary detector may analyze the sound wave signal to detect the boundary of the cleaning area.