The reflection of active waves in a reaction-diffusion equation with spatial inhomogeneity is analyzed by use of the eikonal equation. The counterpart of the Rankine-Hugoniot relation, i.e. the shock condition, is derived for the transition layer in reaction-diffusion systems. In the case that the curvature effect of a wavefront is negligible, we show that the time evolution of a front is well described by Whitham's shock-ray coordinate theory. It is shown that total internal reflection is possible for the speed of a wavefront increasing along a ray.