An electric assembly includes a heat sink defining a through hole and a notch communicating with the through hole; a circuit board defining a fixing hole; and a fastening assembly. The fastening assembly includes a fastener comprising a stem, a head connected one end of the stem, and a clamp connected to an opposite end of the stem; a limiting member comprising a main body slideably disposed on the stem and a limiting portion extending from the main body, the main body received into the through hole, and the limiting portion engageably inserted into the notch; and an elastic member disposed around the stem and between the head and the main body. Wherein the limiting portion is capable of sliding out of the notch and against the heat sink to compress the elastic member.