Introducing mobile manipulators into large working areas has gained importance in the last years. This is due to the fact that manipulators mounted on vehicles have many merits over the ones with fixed bases. The extended workspace and the maneuverability are main advantages of mobile manipulators. However, stability of the system is critical and closely related to the vehicle's motion, arm's motion and the disturbances which may cause the system to tumble. To address the above issue, this paper presents a novel unified dynamic control that keeps the zero moment point (ZMP) on a desired stable position without affecting the end-effector's motion. A redundant scheme is used to develop the motion controller and a novel ZMP disturbance observer is derived to estimate the modeling and inertial errors of the zero moment point to be controlled. Finally, the performance of the proposed controller is validated through dynamic simulation on a 7-dof anthropomorphic arm fixed on differential mobile base. The overall controller not only ensures a good ZMP control for stability but it is also devised to control the end-effector to follow accurately a desired spatial trajectory.