In this paper the active power loss minimization problem is formulated as an optimal power flow (OPF), including equality and inequality nonlinear constraints which represent the power system security conditions. The OPF has been solved using the multiple predictor-corrector interior point method, of the family of higher order interior point methods, enhanced with an optimal computation of the step length. The optimal computation of the primal and dual step sizes minimizes the primal and dual objective function errors, respectively, assuring a continuous decrease of the errors during the iterations of the interior point method. The proposed methodology has been applied to minimize the active power loss of the IEEE-30, IEEE-57. IEEE-118 and IEEE-300 bus test systems. Test results indicate that the convergence is facilitated and the number of iterations may be small.