In the presence of a non-local potential arising from electron–electron interaction, the conventional definition of current density J c=(e/2m)([(p− eA) ψ]* ψ− ψ*[(p− eA) ψ]) cannot satisfy the condition of current conservation, ie, in the steady state. In order to solve this problem, we give a new definition of current density including the contribution due to the non-local potential. We show that the current calculated based on the new definition of current density conserves the current and is the same as that obtained from the Landauer–Büttiker formula. Examples are given to demonstrate our results.