Electroconductive elastomer/carbon allotrope (ECA) composites are used for development of mechanical pressure and gas sensors. Ability of ECA composites to change direct current electrical resistance due to chages of sample geometry is used in these sensors. To carry out further studies of the ECA composites, measurements of the capacitance change depending on mechanical pressure were conducted. The composite samples were tested at different pressures (up to 234 kPa) in the frequency range from 20 Hz to 2 MHz. The ECA composite sample, which contains 10 phr of carbon nanotubes, showed a capacitance reduction of 3.5% (f = 1 kHz, p = 183 kPa). Whereas, the ECA composite sample containing 10 phr of reduced graphene oxide at the same pressure and the same frequency showed no change in capacitance, that is, dC/C0 = 0. Ability to change the capacitance for the mentioned sample changed with increasing frequency and at f = 2 MHz the sample showed the capacitance change of 3.4%. The observed differences in the piezocapacitance effect for the different ECA composite samples could be explained by the significantly different geometry and electrical conductivity of the fillers.