A robot cleaner that automatically removes dust accumulated on a floor while navigating a cleaning area, and a method of controlling the robot cleaner, includes a main body that navigates a floor; a first detector that detects an obstacle getting closer to the main body; an auxiliary cleaner that is mounted on the main body to protrude and retract; a second detector that detects a protrusion state or a retraction state of the auxiliary cleaner; and a controller that determines an abnormal operation of the auxiliary cleaner based on a result of the detection of the second detector and controls a protrusion operation or a retraction operation of the auxiliary cleaner according to a result of the determination.