An armrest assembly mounted on a console of a vehicle may include a console main body provided with a storage box in which a space is formed and installed between a driver seat and a passenger seat of a vehicle, an armrest pivotably installed in the storage box and configured to support an arm of a passenger in the vehicle and open and close an upper portion of the storage box, a button member installed in the console main body and configured to be operated by the passenger to unlock the armrest, an operating unit configured to lock or unlock the armrest from the console main body according to whether the button member is operated, and a console cover configured to cover a portion in which the button member and the operating unit are installed in the console main body and expose an upper end of the button member.