Natural rubber (NR) is an electrostrictive polymer that responds to electrical fields. The permittivity of NR may be increased by doping it with conductive particles. In this study, activated carbon was employed to increase the amounts of free space and interphase charges between a rubber and a filler. Activated carbon was combined in the rubber phase in ratios of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 parts per hundred rubber (phr). The morphology of NR membranes with activated carbon was investigated. In addition, their mechanical, electrical, and electrical response properties were assessed. A proposed preparation method was compared with the conventional preparation method. The results demonstrated that the activated carbon particles blended into NR by the proposed preparation method were distributed homogeneously. When the amount of activated carbon was increased, the dielectric constant increased, but the modulus decreased. The maximum electrostriction coefficient (M33) of the NR membrane with 3.0 phr activated carbon prepared by the proposed preparation method was 3.51 × 10−15 m2/V2. This value was greater than that obtained by the conventional preparation method and close to that of polyurethane, a synthetic polymer material commonly used in actuators.