An exemplary computer case includes an external shell, a circuit board received in the external shell, and a dehumidification device. The circuit board includes a PCI socket providing an auxiliary power supply when the computer shuts down but the computer case retains electrical connection with an external AC power source. The dehumidification device includes a dehumidification card received in the PCI socket for obtaining the auxiliary power supply therefrom and a remote device. The dehumidification card includes a fan for generating airflow to remove moisture from the computer case and a sensor detecting a humidity inside the computer case. The remote device includes a display unit for displaying the result. When the humidity exceeds a predetermined value, the computer is not powered up until the fan evacuates the excess moisture from the computer case and the humidity falls below the predetermined value.