Dynamic mechanical spectroscopy is used to investigate the variation of the glass rubbery transition temperature (Tg) of graphene/polyimide nanocomposites. The Tg was obtained as the temperature corresponding to the peak of the tan δ versus temperature curve for the alpha transition. Cole–Cole curve was constructed for the matrix and the composites composite at 1 Hz and a hemispherical curve was obtained suggesting that the constituents have similar relaxation behavior. The time–temperature superposition principle was used to model the behavior of the nanocomposites at lower frequencies and longer times. Frequency sweep was performed in the range of 0.05–100 Hz at different temperatures. The storage modulus curves obtained at different temperatures (isothermal), as a function of frequency, were shifted horizontally to construct a continuous master curve. Both the generalized reduced gradient method and the Williams–Landel–Ferry (WLF) equation were used to calculate the activation energy for glass–rubber transition. The universal constants C1 and C2 were determined using the WLF equation. The dependence of relaxation time on temperature was verified.