Previous EEG source localization studies in obsessive-compulsive disorder (OCD) reported ambiguous results. The reason probably lies in different OCD samples included in the studies - obsessive-compulsive subjects selected based on a psychopathology questionnaire (the Symptom Checklist - Revised), drug-naïve OCD cases or patients with a long-term disorder. This study was conceived as a replication of our previous research on OCD population coming to treatment in Prague Psychiatric Centre [9]. We included 50 OCD patients (8 drug-free and 42 medicated with SSRIs) and 50 healthy controls. All subjects were different from those enrolled in the previous study. Resting state EEG was analyzed in 8 frequency bands as well as with 1 Hz frequency resolution using the standardized low-resolution electromagnetic tomography (sLORETA). In OCD, sLORETA indicated low-frequency power excess at 2 and 3 Hz in the cingulate gyrus with maximal t-values in Brodmann area 24. The low-frequency activity was unrelated to the severity of clinical symptoms and illness duration but delta power in the right orbitofrontal cortex positively correlated with age of OCD onset. Our results confirm previous finding of the low-frequency excess in the cingulate gyrus in OCD and document the essential role of delta frequencies. Delta activity in the cingulate gyrus is negatively associated with reward-signalling dopamine release in the ventral striatum and increases in states connected with a need for reinforcement. Thus, delta activity could reflect a repetitive need to perform compulsive behaviour in OCD patients.