The motion of dislocations in the high strain rate and dynamic loading regime has been of great interest due to its implication on the plastic deformation in these regimes. Previous theoretical and computational works have shown that dislocations can move faster than the speed of sound since it remains challenging to track and measure these fast-moving dislocations experimentally. However, the majority of these works focus on dislocations in face-centered-cubic (FCC) and body-centered-cubic metals (BCC). In this work, the dislocation mobilities of basal edge, basal screw, prismatic edge, and prismatic screw dislocations in Mg in the sub-, tran- and supersonic regimes are studied using molecular dynamics simulations. We found that only prismatic edge dislocations can achieve supersonic velocities. Importantly, it was discovered that the limiting velocities for Mg greatly depend on the hydrostatic stress around the dislocation core, which causes the discrepancy between the theoretical calculations (via elastic constants) and MD simulated results.