Carbon xerogel was prepared by a sol–gel technique by mixing formaldehyde with dissolved resorcinol in acetone solution using picric acid as a catalyst, followed by pyrolysis treatment at the desired temperature. X-ray diffraction analysis revealed that the obtained product has an amorphous phase, with an average grain size of approximately 2 nm. Scanning electron microscopy showed the existence of a mesoporous structure in the resorcinol–formaldehyde (RF) matrix with a pore size of about 50 nm. The electrical measurements carried out on our material showed interesting results. In fact, DC conductivity indicated that the xerogel is transformed from an insulating phase to a carbon-conducting phase under the pyrolysis tem- perature effect. The current–voltage (I–V) characteristics of the sample prepared at 650°C show different regions—an ohmic region at low applied voltages and a negative differential resistance (NDR) region at higher voltages, with the NDR phase appearing above a threshold voltage. Also, a hysteresis effect depending on the synthesis and measurement parameters was observed. The observed behaviors are explained in terms of the filament formation phenomenon and the Joule heating effect. These interesting behaviors are promising for threshold switching and neuromorphic computing applications.