Electrical transport and magnetization measurements were carried out on a ceramic samples of La0.5Pb0.5MnO3 and La0.5Pb0.5MnO3 containing 10 at. % of Ag in a dispersed form. The resistivity (rho) at zero applied magnetic field exhibits a shallow minimum at the temperature T similar to 25 divided by 30 K. This minimum shifts towards lower T upon applying a magnetic field (H) and disappears at a certain field H-cr, while residual resistivity decreases notably with increasing of H. It is found that the bulk-scattering model is not adequate for describing of such behavior of rho in the presence of H, It seems that the proposed model of charge-carrier tunneling between antiferromagnetically coupled grains accounts for the results obtained.