The dark side of ICT usage has started receiving increasing attention in recent years. As the Internet allows anonymity, some individuals are making use of social dating websites to engage in extramarital cyber affairs. In this study, we investigate factors likely to mitigate people’s engagement in cyber affairs. We focus on the influence of religious beliefs by analysing US data over one year, drawn from a large dating website set up to facilitate married persons in establishing extramarital, offline companionships. Our main finding is that increased religiosity decreases cyber affair activities—after controlling other factors, the average expenses on cyber affairs by users from areas with more religious adherents becomes smaller. However, the mitigation effect weakens when religious rules concerning marriage are overly strict. Spending on cyber affair related activities is higher in countries with higher concentrations of Catholics relative to Protestants or Evangelical Christians. Further, entertainment facilities such as bars distract people from engaging in cyber affairs—expenses on cyber affair related activities actually decrease in counties with more bars. Our study provides several new insights into the relationship between religiosity and engagement in cyber affairs.