A stand-by mode management module applied in a computer system having a BIOS (basic input/output system), a graphic module and a display module is provided. The computer system is operated in a working state and at least one stand-by state. The module includes a timer and an interrupt generation unit. The timer starts a count period when detecting that the computer system is idle. The interrupt generation unit generates an interrupt request to the BIOS to request the computer system to prepare to enter to a specific state when the count period is reached. When the specific state is entered, the computer system enters the stand-by state, a PLL (phase lock loop) of the display module keeps turning on, and PLLs other than the PLL of the display module are turned off and the graphic module acquires a frame stored in a fixed area of a storing unit and displays the acquired frame on the display module.