We report on the effects of temperature and dc magnetic field on non-resonant microwave absorption measurements at X-band (8.8–9.8 GHz) in Pb(Fe2/3W1/3)O3 powders, for the 294–425 K temperature range. Two techniques are used: the magnetically modulated microwave absorption spectroscopy (MAMMAS) and the low-field microwave absorption (LFMA). MAMMAS response showed distinctive features associated with para-antiferromagnetic transition at T N =334.3 K, and below T N a weak ferromagnetism is also observed, and it is attributed to canting of Fe+3 ion sublattices in the antiferromagnetic matrix. The low-field microwave absorption (LFMA) is used to give further knowledge on this material, where this technique also gives evidence of the magnetic transition, suggesting a weak ferromagnetism at room temperature.