Disclosed is a method and device for controlling power in a mobile Internet terminal which includes a transmitter and a receiver for transmitting and receiving frames each consisting of an uplink frame and a downlink frame to and from a base station. The method includes the steps of receiving information as to whether effective data is present in the uplink frame or the downlink frame from the base station; supplying power to the transmitter during a period in which effective uplink data is present according to the received information; and supplying power to the receiver during a period in which effective downlink data is present according to the received information. The device also includes a power controller for receiving information as to whether effective data is present, and supplying power to the transmitter or receiver during a period in which effective uplink data or downlink data are respectively present.