A system of threshold aerogel Cherenkov counters with refractive index n = 1.05 has been tested. This system has been designed for e/π separation with energies of up to 450 MeV in experiments aimed at measuring cross sections of e +e −-annihilation into hadrons with the SND detector at the VEPP-2000 collider. The characteristics of the system are presented. The measurements have been taken using electrons and muons from e +e − → e +e − and e +e − → μ+μ− reactions at beam energies of 250–500 MeV. If the mean signal from electrons in the counter is 3.5 photoelectrons, the detection efficiency for electrons is 0.955.