A computer system includes an identification device and a host. The identification device includes a first wireless module for receiving a radio identification signal and then emitting a radio user signal with an identification code. The host includes a processing module for controlling operation of the host, a second wireless module for emitting the radio identified signal and receiving the user signal, a power supply for supplying power to the processing module while receiving a power control signal, and a control module electrically connected to the power supply. Before the power supply supplies power to the processing module, the control module checks whether the identification code within the user signal matches a predetermined identification code as the second wireless module receives the user signal. If the identification code within the user signal matches the predetermined identification code, the control module can transmit the power control signal to the power supply.