Disclosed are a robot arm having high back-drivability to interact with a human being, which is safely stopped, and a method of controlling the robot arm. When the operation of the robot arm having high back-drivability to interact with a human being is converted into a safety mode due to the occurrence of an emergency, in which the operation of the robot arm is stopped, only a torque having a degree to compensate for gravity applied to the robot arm, i.e., only a torque to maintain the kinematical position of the current state of the robot arm without falling of the robot arm due to gravity, is outputted to control the robot arm as if the robot arm is in a weightless state, thus being capable of safely stopping the robot arm.