We have observed large 4d moments on isolated Mo atoms at substitutional and octahedral interstitial lattice sites in Yb metal, showing Curie-Weiss local susceptibility and a Korringa-like spin relaxation rate. The interstitial Mo atoms, despite strong hybridization with the Yb neighbors, show rather small Kondo temperature ( T(K)</=60 K), implying high moment stability. While magnetism of Mo at the substitutional site is consistent with Kondo-type d-sp interaction, we suggest that moment stability at the interstitial site is strongly influenced by ferromagnetic polarization of Yb-4f5d band electrons.