A two-step electric current measuring technique used by the authors in previous works is here detailed for the first time. This technique allows measuring the electric conduction currents that are overridden by orders of magnitude larger displacement currents. By performing two sets of measurements, the technique allows to cancel out the displacement currents, retrieving only the conduction currents from the measurements. In this work, the technique is applied in the study of the electrical conduction of mineral oil-based nanofluids prepared with surface modified ZnO nanoparticles. The results show that the ZnO nanoparticles introduce charge generation mechanisms within the mineral oil that increases the measured conduction currents, in agreement with the literature.