The unsteady movement of viruses outside buildings is simulated by the method of large eddy simulation (LES). The virus source originated in a room with infective patients is described by the non-linear population dynamic model of virus infection. Considering the indoor virus emitting outside from windows, the emitting viruses are moving with airflow around buildings. The Smagorinsky-Lilly model is adopted to represent the subgrid-scale stresses resulting from the filtering operation. The unsteady movement of viruses is governed by the passive scalar convection-dispersion equation, where the subgrid-scale eddy diffusivity is fixed by the subgrid eddy viscosity divided by a constant turbulent Prandtl number. By assuming no secondary infection, the time-dependent concentration of virus around buildings is obtained and the infectious area is determined with the known pathogenic concentration. The present research is useful for forecasting and controlling the spread of airborne disease virus around buildings.