An electronic device includes a main body and a number of fan modules. The main body defines a number of vents in a top of the main body. The fan modules are mounted to the top of the main body. Each fan module includes a housing and a fan. The housing includes a side plate defining an opening aligned with the vents. A stop plate is pivotably connected to a first end of the opening, and is operable to cover the opening. The fan is mounted in the housing, and is near a second end of the opening opposite to the first end.