A fixing device includes a stationary frame and a number of elongated resilient tabs. The stationary frame defines a central axis and includes four sidewalls for receiving a number of magnets. Each sidewall includes a receiving hole and at least one protrusion formed on each sidewall at a lower portion thereof. A slot is defined in each protrusion. The tabs correspond to the magnets. Each tab includes an engagement portion, an angled portion, and a contact portion. The angled portion is interconnected between the engagement portion and the contact portion. The engagement portions engage in the respective slots. The contact portions resiliently abut against the corresponding magnets. Each tab is configured to apply a force on the corresponding magnet in a direction toward the central axis.