Inhibitory control processes are indispensable for goal-directed behavior. On a neurophysiological level, theta band power has been suggested to be important during inhibitory control as well as proactive control processes. Here we ask whether theta activity in the pre-trial/between-trial time period, reflects proactive control that correlates with theta activity in the upcoming trial. Theoretical considerations also suggest that such a correlation is modulated by the demands on inhibition. To investigate these questions, we conducted an EEG study using a Go/Nogo task in which demands on inhibitory control are varied. We used different EEG beamforming approaches to focus the analysis on the functional neuroanatomical level. We show that theta band activity in the ventromedial prefrontal cortex (vmPFC, BA10) is associated with the proactive control in the pre-trial interval and correlates with theta-related processes in the right inferior frontal gyrus (rIFG, BA45) during response inhibition. In addition, we show that demands on inhibitory control modulate the inter-relation between proactive vmPFC and inhibitory control-related rIFG-theta activity. Such effects were not observed for beta frequency activity. The study is the first to emphasize the relevance of pre-trial (proactive) vmPFC theta-band activity during inhibitory control in humans. It is shown that pre-trial activity, which is often neglected in EEG research, provides valuable information about the neuronal dynamics of cognitive control.