Presenting unpaired unconditional stimuli (US) during extinction training reduces the renewal of conditional fear due to context change and slows re-acquisition. The present study investigated whether this reduced return of fear is mediated by Pavlovian inhibitory conditioning to the conditional stimulus paired with the US during acquisition (CS+) that is acquired when this stimulus is presented without the US in an excitatory extinction context. Using an ABA renewal paradigm that trained extinction in a context different from acquisition and renewal test, participants either received no USs (Standard), five unsignalled US presentations (Unsignalled) or five presentations of the US preceded by a novel, third CS (Signalled) during extinction training. Extinction was followed by tests for renewal and re-acquisition. Replicating previous results, renewal of electrodermal conditional responses was observed in group Standard, but not in group Unsignalled. Signalling the additional USs, and thus reducing context conditioning and the potential for inhibitory conditioning, did not reduce their effect in that renewal was absent in group Signalled. These results are inconsistent with an inhibitory conditioning account of the effects of unpaired US presentations during extinction. A trial sequence learning account or an arousal account may explain the effects of unpaired presentations of the US during extinction.