A tight-binding model of the electronic structure of substitutional nitrogen in GaAs, together with a variational description of quasilocalized nitrogen-induced electronic states near the conduction band edge, is used to calculate the nitrogen-related alloy scattering of conduction band electrons in the dilute nitride alloy, GaNxAs1−x. The electron mobility in the nondegenerate and degenerate doping regimes is calculated for bulk and quantum well geometries from the energy-dependent scattering rate using the Boltzmann transport equation in the relaxation-time approximation. Nitrogen cluster states are found to dominate the scattering near the conduction band edge and play a crucial role in limiting the electron mobility. In the experimentally relevant regime of degenerate doping and at nitrogen concentrations of 1 to 2%, the room-temperature mobility is found to be limited to values less than 300 cm2(V s)−1, in agreement with experimental measurements.