A method and an apparatus for controlling a sleep mode in a portable terminal having a main controller and a sub-controller operating at low power are provided. The method includes detecting, by the sub-controller, a motion signal generated by a camera when the main controller enters the sleep mode, extracting a motion pattern from the detected motion signal, determining whether the extracted motion pattern is substantially identical with a preset motion wake-up pattern, and cancelling the sleep mode by waking-up the main controller when the extracted motion pattern is substantially identical with the motion wake-up pattern.