For glasses in the Ag₂Se-As₂Se₃-GeSe2 system, the concentration dependences of density and softening point and the temperature dependences of dc and ac electric conductivities are studied. The composition region is found that features anomalously strong concentration dependence of electric conductivity. This phenomenon is discussed in terms of the percolation theory. The size of high-conductivity microregions is estimated at 60-80 nm.