A portable electronic device including a touch screen, a micro processing unit, a central processor and a display is provided. The central processor can operate in a normal operation mode or a sleep mode. The touch screen overlays the display, and includes a first touch area, a second touch area and at least one electrode. When the central processor operates in the sleep mode and one of the first and second touch areas senses a touch, the at least one electrode generates a touch signal. The micro processing unit determines whether the touch is sensed by the first or the second touch area according to the touch signal. If the touch is sensed by the second touch area, the micro processing unit outputs a wake-up signal to the central processing unit, so as to switch the central processor from the sleep mode to the normal operation mode.