It has been proposed that the extinction of conditioned fear and the instructed regulation of emotion engage common ventromedial prefrontal (vmPFC) circuitry, indicating common underlying processes. Here we report an fMRI study using a novel task designed to investigate the neural overlap between cognitive emotion regulation and extinction of conditioned fear in a simple and controlled way. Participants were conditioned to expect an electric shock during the presentation of one of two letters (CS+ and CS-). In a second phase, the same letters were presented within words belonging to two distinct semantic categories. Participants were told that one of these categories would indicate safety from shock. We hypothesised that cognitive processing of words from the safety category would lead participants to engage neural circuitry involved in extinction and learned safety, and lead to reduced conditioned responses in limbic circuitry. The contrast between safe and dangerous CS+ trials revealed activation in a network of brain regions including left inferior frontal gyrus, as well as bilateral temporal and parietal cortices, though no activation in vmPFC was observed. Clusters in bilateral insula and anterior cingulate cortex (ACC), part of the network typically associated with anticipation and experience of pain, showed activation for dangerous CS+ trials that was reduced for safe CS+ trials. These results suggest that the task elicited the expected aversive conditioned response during trials that remained dangerous, whereas a semantically based cognitive control mechanism down-regulated this response during safe trials. Results from this task were also compared with those from a modified version of an instructed emotion regulation task using negative IAPS images as affective stimuli. A voxelwise conjunction analysis showed no significant overlap between the two tasks, suggesting that the neural mechanisms involved in both types of emotion regulation may be largely distinct.