Recent studies have shown mixed findings regarding the relationship between network heterogeneity on social media and opinion polarization. Focusing on individual-level variables (i.e., individuals' political orientation, fear of a risky situation, and fear of an out-group), the objective of this study was to investigate opinion polarization over North Korean issues that have brought out threats to South Koreans and tangled with political orientations in the nation. Our analysis indicated that network heterogeneity on social media could decrease polarization. Moderation effects of political orientation and fear of political opponents in the relationship between network heterogeneity and polarization were also found. Findings of this study extend previous discussions regarding the relationship between network heterogeneity and polarization in the context of social media by concentrating on North Korea's threatening situation.