The α relaxation associated with the glass transition region of a thermosetting powder coating was studied within a range of measuring frequencies ( f) between 100 kHz and 3 mHz. The thermoset was based on a carboxyl-terminated polyester crosslinked with a triglycidylisocyanurate. The relaxation was studied by dielectric analysis (DEA) (1 Hz–100 kHz), dynamic mechanical thermal analysis (DMTA) (10 mHz–100 Hz), and temperature-modulated differential scanning calorimetry (TMDSC) (3–33 mHz). Additionally, experiments of intrinsic cycles by DSC were performed to study the structural relaxation and to determine the reduced apparent activation energy, which was 126 kK. The correlation of data was studied in a relaxation map, in which the ln(average relaxation time 〈 τ〉) (〈 τ〉 = 1/(2 πf) was plotted against the reciprocal of the relaxation temperature, which was determined by the maximum in tan δ and the loss permittivity ɛ″ by DMTA and DEA, respectively, and by the midpoint of the variation in the modulus of the complex heat capacity by TMDSC. The relaxation times obtained by TMDSC appear as an extrapolation of those obtained by DEA, while the DMTA relaxation times are slightly higher than those of DEA. The DMTA results were fitted to a Williams–Landel–Ferry equation ( C 1 = 7.905 K and C 2 = 51.46 K) and the dielectric data to a Vogel–Tamman–Fulcher equation (ln A = −30.33 s, B = 1552 K and T 2 = 305 K). The curves of both equations were coincident within the range of the highest relaxation times.