The dynamics of plasticity is considered based on the field theoretical approach developed by physical mesomechanics. The equation of motion governing mesoscopic volume elements in plastically deforming media is derived from the mesomechanical field equation. Theoretical analysis on this equation of motion indicates that in the plastic regime solid-state media exert two types of forces; the restoring force and energy dissipating force. The former is associated with the shear modulus, and causes the displacement field to be oscillatory. The latter is associated with a quantity analogous to the electric charge, and causes the displacement field to be decaying. Experimental observations that support these theoretical considerations are presented.