We report the effect of static electric fields in different geometrical features on the collisional ionization of helium atoms by antiproton. The Classical Trajectory Monte Carlo (CTMC) method with a model interaction potential has been used to simulate the differential and total ionization cross sections in antiproton–helium atom collisions in the energy range of 10–500keV with and without electric fields. The calculated ionization cross sections are in reasonable agreement with the recently reported experimental and theoretical results. The effects of the external electric fields are seen to be quite prominent.