An optical mouse apparatus includes a light source unit, a sensing unit, and a processing unit. The light source unit is arranged for generating and emitting an optical signal, wherein the optical signal is emitted upon a surface, and then reflected to form an optical reflected signal. The sensing unit is arranged for generating a sensed image output according to the optical reflected signal, wherein the sensed image output is utilized for estimating an image displacement of the optical mouse apparatus. The processing unit is coupled to the light source unit and the sensing unit, and arranged for controlling the light source unit to emit the optical signal and determining a operation status of the optical mouse apparatus according to an image variation of at least a partial region of each of consecutive images of the sensed image output.