The invention discloses a mobile device, and an antenna assembly used for a mobile device. The antenna assembly comprises a cavity, an exciting element, and a frequency deviation structure. The cavity is an internal space formed by connecting a metal frame, a metal bottom plate and a metal cover plate, and the cavity has an opening. The exciting element is arranged in the cavity or at the opening of the cavity, and is used for exciting the cavity to generate multiple resonant frequencies corresponding to multiple characteristic modes. The frequency deviation structure is used for enabling at least one resonant frequency to be deviated. The invention also provides the mobile device with the antenna assembly. By additionally providing the frequency deviation structure, the position, shape or other characteristics of the deviation structure can be adjusted by need, so as to adjust the characteristic modes of the cavity. By the exciting element, the cavity is enabled to generate corresponding resonant frequencies under different characteristic modes, so that the effect of deviating the resonant frequency is achieved.