Response inhibition processes are important for goal-directed behavior and particularly demanded when it is unlikely to inhibit automatically executed responses. It has been suggested that the norepinephrine (NE) system is important to consider for such likelihood effects. As an indirect measure of the NE system activity we used the pupil diameter and integrated this data with neurophysiological (EEG) data and beamforming analyses. The study shows that inhibitory control processes reflected by theta oscillations are strongly modulated by the likelihood to employ these processes and that these mechanisms were related to neural processes in the SMA and SFG. Probably, the modulations observed for theta band activity may reflect modulations in the encoding of a surprise, or conflict signal. Interestingly, correlation analyses of neuronal activity at the sensor and the source level with pupil diameter data revealed strong correlations that were only seen in the condition where inhibitory control processes were rarely demanded. On the basis of findings and theoretical models suggesting that the pupil diameter can be interpreted as a proximate of NE system activity the results may be interpreted that the NE system modulates inhibitory control processes via theta band activity in the SFB when the likelihood to inhibit a prepotent response tendency is low. From this it may be speculated that the NE system dynamically gains and loses relevance to modulate inhibitory control depending on boundary conditions that determine the mode of responding.