A novel ternary nanocomposite consisting of activated carbon (AC) and titanium dioxide (TiO2) decoration in the presence of reduced graphene oxide (TiO2-rGO-AC) was fabricated by a facile hydrothermal synthesis method for use as a high-performance photocatalyst. The as-prepared TiO2-rGO-AC nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. The results demonstrated that the TiO2 and activated carbon were well dispersed on the rGO surface. The photocatalytic performance of the TiO2-rGO-AC nanocomposite was evaluated as a catalyst for the photodegradation of rhodamine B. The degradation rate was 3.4 times higher than that of pure TiO2 under simulated solar light irradiation. The enhancement of photocatalytic performance is attributed to the adsorption of AC which significantly increased the organic molecule concentration near the catalytic surface, allowing the effective transfer and separation of photogenerated electrons. TiO2-rGO-AC photocatalyst is also effective for the degradation of tetracycline in aqueous solution, suggesting wide application of these nanocomposite materials in various fields including air purification and wastewater treatment.