New advanced multi-phase γ-TiAl based alloys (TiAl-Nb-Mo), so called TNM alloys, have been developed to promote hot workability and to allow easier processing by conventional forging. However, to control and stabilize the final microstructure, specific processing and further thermal treatments are required. In the present work we used mechanical spectroscopy techniques to obtain a better understanding of the microstructural mechanisms taking place at high temperature applying two different heat treatments. Internal friction spectra and dynamic modulus evolution have been measured in an inverted torsion pendulum up to 1220 K. A stable relaxation peak was observed in both cases at about 1050 K for 1 Hz. Spectra acquired at several frequencies between 0.01 Hz and 3 Hz allow us to measure the activation parameters of this peak. In addition, a high temperature background (HTB) has been observed. This HTB, which has been found to be dependent on thermal treatments, has been analyzed to obtain the apparent activation enthalpy, which seems to be correlated to the creep behavior. Finally, we discuss the relaxation peak and the HTB in terms of the microstructural evolution during thermal treatments.