A method and apparatus for performing air/fuel ratio feedback control for an internal combustion engine by comparing the results of the two comparisons; (a) comparing a determined (i.e., decision) value with a measured value detected by an oxygen sensor, and (b) comparing the determined value with a reference value, so as to determine if either is relatively large or small. Further included is an arrangement for determining whether the determined value coincides with the measured value as well as whether it coincides with the reference value, and then increasing or decreasing the determined value in accordance with the result of the determination (comparison), thereby correcting an abnormal condition of the determined (i.e., decision) value whenever the determined value is displaced from a normal condition due to injected random noise.