The shear viscosity of liquid Na–K alloys is computed from molecular dynamics simulations using the Green–Kubo formalism. Interatomic interactions are described using effective pair potentials obtained from Fiolhais pseudo-potential and self-consistent screening. The composition dependence of the viscosity is first investigated at 373 K, then its temperature dependence at three different compositions, namely Na10–K90, Na50–K50, and Na90–K10. Simulation results are first compared with available experimental data. The evolution of the viscosity of the alloys versus temperature is similar to that of a pure one component fluid. This is discussed in connection with the chemical order of the mixtures.