In this study, dynamics and stability of a novel hybrid serial-parallel mobile robot is elaborated. This robot compounds of a differentially-driven wheeled platform, a novel spatial parallel mechanism, and a serial manipulator arm. Using a moving parallel mechanism as the base of a serial manipulator makes the system capable to carry heavy payloads, and prevents tipping over of the system. In those cases that robot must perform tasks on uneven terrains with unknown obstacles and disturbances; this system is able to change its configuration to move safely. Spatial parallel mechanism has three degree-of-freedom (DOF) and uses three planar prismatic actuators along linear axes. So, the endeffector of parallel mechanism has a fixed orientation and only has translation motion relative to mobile base. In this paper, dynamic, and kinematics redundancy of this robot is investigated. Tipover stability of the robot will be investigated using the newly proposed Moment Height Stability (MHS) measure. This robot is able to compensate tipover instability and thus can carry more heavy objects. Effectiveness of the parallel mechanism in compensating tipover instability is illustrated in two maneuvers.