In this paper, we present the tip-over prevention technique using a control moment gyro for a holonomic omnidirectional mobile robot with active dual wheel caster assemblies. With concern to the sudden dynamic changes during maneuver, the dynamical model is derived and used together with the force-angle stability measure (FASM) to estimate the tip-over incident and the tipping direction. A single gimbal control moment gyro (SGCMG) is proposed to counter the instability by producing a precession torque in the opposite direction of the estimated tip-over direction. Simulation results are given to demonstrate the performance of this approach.