The low-fear model of primary psychopathy has been supported by empirical findings such as attenuated physiological arousal in anticipation of threatening stimuli. The somatic marker hypothesis proposes that salient changes in the bodily state are processed as signals of whether a situation is good or bad and guide an individual to avoid potential adverse consequences. The present study aimed to elucidate the role that attenuated physiological arousal plays in the relationship between primary psychopathy and fairness norm violations both under the threat of punishment and under no potential for punishment. Primary psychopathy was associated with an attenuated skin conductance response prior to the choice of unfair monetary offers to another person, regardless of the potential for punishment. Attenuated skin conductance mediated the association between primary psychopathy and the choice of an unfair offer, especially in the no-punishment condition. However, in the punishment condition, primary psychopathy significantly predicted the choice of unfair offers even after controlling for the magnitude of skin conductance. The bodily response may have only a marginal effect on interpersonal decision-making under a threat of punishment. The present results suggest that the low-fear account of social norm violations as a function of primary psychopathy should be re-discussed.