This paper describes a strategy for the measurement of boundary mobility using molecular dynamics (MD) simulations and its application to the migration of nominally flat 〈001〉 tilt grain boundaries in nickel, as described using an EAM potential. Determination of the driving force for boundary migration requires proper accounting for non-linear elastic effects for strains of the magnitude needed for MD simulation of stress-driven boundary migration. The grain boundary velocity was found to be a non-linear function of driving force, especially at low temperature. However, extrapolation of the data to small driving force allows for the determination of the mobility at all temperatures. The activation energy for grain boundary migration was found to be 0.26 eV. This demonstrates that boundary migration in pure metals is not athermal, but the activation energy is much smaller than expected based upon experimental measurements. This discrepancy is similar to that found in earlier simulation measurements.