Magnetic properties of the R(1.03)Co(10)Mo(1.94) systems, where R = Y, Gd-Lu with the tetragonal ThMn12-type structure (R = heavy lanthanides), have been investigated in the temperature range 4.2-1000 K in magnetic fields up to 14 T at low temperature. All these compounds are ferrimagnetic below about 500-600 K, with the exception of the Y- and Lu-containing compounds, which are ferromagnetic.