There is increasing evidence that the strength of the relation between slow (SW) and fast (FW) wave activity in the EEG is associated with specific motivational states and their corresponding neuroendocrine patterns. Enhanced correlations between SW and FW have been related to anxiety, behavioral inhibition and high basal cortisol levels. However, the direct effects of cortisol on SW-FW coupling have not been experimentally studied yet. The present study investigated whether cortisol administration increases SW-FW coupling. Resting state EEG recordings were obtained from 40 right-handed healthy male subjects with extreme low or high scores on a behavioral inhibition scale, after placebo and cortisol (50 mg) administration. As expected, cortisol resulted in a significant increase in correlation between SW (delta) and FW (beta) activity compared to placebo. In addition, delta-beta correlation was significantly higher in high compared to low behaviorally inhibited subjects in both conditions. These results suggest that cortisol can modify brain activity, increasing a pattern associated with anxiety and behavioral inhibition. This is in line with findings associating cortisol with behavioral inhibition and anxiety.