Equivalent electric circuits allowing the simulation of the behavior of nanocomposites based on thermosetting resin and nanocarbon filler are presented. The electric circuits are constructed by employing a multistep simple procedure in which the values and number of the parameters are adjusted until a suitable criterion, based on the comparison between simulated and experimental frequency spectra is satisfied. A resistance-capacitance (RC) simple parallel branch in parallel with a variable number of RC series branches is shown to be capable to reproduce the frequency response of a prepercolative carbon black and two carbon nanotube (CNT) nanocomposites with CNT concentration close to the percolation threshold. The obtained equivalent circuits may be employed for the interpretation of the physical mechanisms underlying the electromagnetic (EM) behavior. Moreover, they can be used in circuit simulators for first-approximation design of EM devices based on such composites.