Yes there is, both a separate desk inside in the main rental area, or if you're feeling brave there's a Gold office in the lot. If it's your first time renting at JNB then head to the main rental area and use the Gold desk there, but if you're coming from domestic arrivals it's quicker to take the first bridge to the parkade and then head up to level 2, go into the garage and you'll see the yellow Hertz office.