Depression is an affective disorder, which symptoms might often be considered as exclusively mood related. However, most of depressive patients report massive psychological strain because of cognitive deficits, which even last in the remission state. In the past, the frontal midline theta oscillatory activity in the electroencephalogram (EEG) was associated with cognitive control processes. Therefore, the aim of our study was to examine theta power differences between healthy controls (HC) and patients with major depression (MD) when cognitive control is needed. For this reason, 36 matched participants (each group) performed a verbal Eriksen-Flanker-Task while an EEG was recorded. The preliminary results showed that HC compared to MD patients show a stronger increase of total, evoked and induced theta power comparing the non-conflict trials with the conflict trials. In the HC group, a lower increase of theta power was associated with a stronger flanker effect in reaction time and subclinical depressive symptoms (BDI-II). Furthermore, the theta increase was positively associated with a better performance in other executive control tasks (Go/Nogo-, n-Back-Task) in both examined groups. These results indicate that theta power changes could be a marker for abnormal oscillatory changes in people suffering from MD. HC are able to recruit cognitive control resources more efficiently in the conflicting trials compared to MD patients. These electrophysiological findings support the relevance of considering more seriously the cognitive syndrome in depression.