<p>A flat flame of a methane-air mixture was numerically simulated in a longitudinal electric field at various fuel/air ratios. A computational code developed in the OpenFOAM based on the reactingParcelFoam solver was used for numerical calculations. The results showed that the predicted value of the ion current correlates with the experimental data. The best agreement is achieved in the lean (<i>φ</i> ≤ 0.8) and rich (<i>φ</i> ≥ 1.3) flames. The greatest discrepancy is recorded for the regime of fuel/air equivalence ratio <i>φ</i> = 0.9. The maximum ion current is achieved at <i>φ</i> = 1.1, which corresponds to the experimental results. The obtained data demonstrate the adequacy of the developed code in predicting the flame current value. Calculation data indicate an increase in CH concentration by 20.5 % and O concentration by 2.0 % when exposed to the electric field; the interaction of these components is the initiating reaction for the formation of charged particles in hydrocarbon flames.</p>