An ensemble average approach is proposed for determining the temperature and thermal equilibrium state of individual atoms in solids modeled using nonequilibrium molecular dynamics simulations (NEMD). The basic assumption of the approach is that the atomic velocity of an atom is the sum of a mean mechanical velocity and a random thermal velocity, which can be separated by performing ensemble average of many realizations of the same ensemble. Mechanical and thermal energy field obtained from the decomposed thermal and mechanical velocity together with the thermal velocity distribution reveal the details of energy transfer in these nonequilibrium processes.