Measurements have been made at 4.2-30 K for the thermal conductivity of a poly-crystalline Fe-25Mn-5Al-0.2C sample with negative temperature coefficient of resistivity. It is found that the phonon conductivity is anomalously proportional to T. The suggested explanation is that this phenomenon results from the noneffectiveness of the scattering of phonons by electrons, when electrons have short mean free path caused by addition of Al.