We have observed for the first time non-thermal relaxation of the surface stress of Si induced by electron irradiation at room temperature. An atomically thin disordered layer was introduced by Ar ion bombardment. The surface stress change during the ion bombardment and the following electron irradiation of Si(100) was measured by means of an optical microcantilever technique. We have found that the compressive stress in the Si surface due to the disorder induced by ion bombardment was completely relaxed by electron irradiation at low energy. The criterion for complete relaxation is found not to be total energy deposition, but number of irradiated electrons.