A mobile device for enhancing antenna stability includes a nonconductive frame, a back cover, a PIFA (Planar Inverted F Antenna), and a U-shaped ground element. The PIFA is disposed between the nonconductive frame and the back cover. The U-shaped ground element is coupled to the PIFA, and is at least partially attached to the nonconductive frame. The vertical projection of the PIFA at least partially overlaps the U-shaped ground element.