The activation energy associated with bulk electrical conduction in functional materials is an important quantity which is often determined by impedance spectroscopy using an Arrhenius-type equation. This is achieved by linear fitting of bulk conductivity obtained from complex (Z*) impedance plots versus T⁻¹ which gives an activation energy E_a(σ) or by linear fitting of the characteristic frequency f_max obtained from the large Debye peak in M′′–log f spectroscopic plots against T⁻¹ which gives an activation energy E_a(f_max). We report an analysis of E_a(σ) and E_a(f_max) values for some typical non-ferroelectric and ferroelectric materials and employ numerical simulations to investigate combinations of different conductivity–temperature and permittivity–temperature profiles on the log f_max–T⁻¹ relationship and E_a(f_max). Results show the log f_max–T⁻¹ relationship and E_a(f_max) are strongly dependent on the permittivity–temperature profile and the temperature range measured relative to T_m (temperature of the permittivity maximum). Ferroelectric materials with a sharp permittivity peak can result in non-linear log f_max–T⁻¹ plots in the vicinity of T_m. In cases where data are obtained either well above or below T_m, linear log f_max–T⁻¹ plots can be obtained but overestimate or underestimate the activation energy for conduction, respectively. It is therefore not recommended to use E_a(f_max) to obtain the activation energy for bulk conduction in ferroelectric materials, instead E_a(σ) should be used.