Differences in fear conditioning between individuals suffering from chronic pain and healthy controls may indicate a learning bias that contributes to the acquisition and persistence of chronic pain. However, evidence from lab-controlled conditioning studies is sparse and previous experiments have produced inconsistent findings. Twenty-five participants suffering from chronic back pain and twenty-five controls not reporting chronic pain took part in a differential fear conditioning experiment measuring attention (eye tracking) and autonomic arousal (pupil dilation and skin conductance) elicited by visual cues predicting the presence or absence of electric shock. In contrast to the healthy control group, participants with chronic pain did not acquire differential autonomic responding to cues of threat and safety and specifically failed to acquire any attentional preference for the safety cue over irrelevant contextual cues (while such preference was intact for the threat cue). We present simulations of a reinforcement learning model to show how the pattern of data can be explained by assuming that participants with chronic pain might have experienced less positive emotion (relief) when the electric shock was absent following safety cues. Our model shows how this assumption can explain both, reduced differential responding to cues of threat and safety as well as less selective attention to the safety cue.