The electropolymerization of o-phenylenediamine was performed on an electrochemically reduced graphene oxide (E-RGO)/glass carbon electrode (GCE) (E-RGO/GCE). It was found that this novel poly(o-phenylenediamine) (PoPD)/E-RGO (PoPD/E-RGO) hybrid composite showed good electrocatalytic activity toward dopamine (DA) and good specificity for the detection of DA without interference from ascorbic acid (AA) or uric acid (UA). Differential pulse voltammetry was used for the electrochemical DA detection. The response peak current for the electrochemical sensor was linear over the ranges of 10 to 400 μM (r = 0.996) and 400 μM to 800 μM (r = 0.997). The detection limit was estimated to be 7.5 μM. The electrochemical sensor also exhibited good stability. In addition, the electrochemical sensor was successfully applied to the detection of DA in human urine samples using the standard adding method with satisfactory results.