Fe3Al intermetallic compounds and several (Fe,Cr)3Al alloys with Cr content from 3 to 25 % have been studied using isothermal mechanical spectroscopy. The Zener relaxation caused by reorientation of pairs of substitute atoms in Fe is observed in all studied alloys and used to evaluate the activation parameters of Al (Cr) atom jumps in Fe. The second internal friction peak at higher temperatures was observed only in Cr containing alloys. Isothermal mechanical spectroscopy (employed frequency from 10-4 to 102 Hz) gives some advantages as compared with ordinary techniques, i.e. study of anelasticity as a function of temperature. It allows to avoid transient effects and to measure materials in a state close to equilibrium. This allows to distinguish clearly between Al atom diffusion in Fe3Al in B2 and D03 states (activation energies for Fe – 26 Al in the B2 range the HB2 ≈ 235 kJ/mol, and in the D03 ordered range the HD03 ≈ 286 kJ/mol). Effect of chromium on the Zener relaxation is analysed.