The kinematics and equations of motion of an equivalent single-degree-of-freedom system for a moving dislocation in a modified Frenkel-Kontorova linear-chain model are derived and then used in conjunction with computer simulation runs. The average drag force on a moving dislocation at zero temperature (lattice drag force) is computed for a range of dislocation velocities. At a velocity comparable with the loss-free velocity, obtained by Earmme and Weiner from a steady-state solution, we obtain a minimum value for the lattice drag force. For velocities above the loss-free velocity the results agree with those obtained fom steady-state solutions by Earmme and Weiner. Below the loss-free velocity the lattice drag force is relatively small. It goes through a maximum which is of the order of 10−4 times the interatomic spring constant k1 of the model.