While focus group discussions have become popular across the communication research field, some researchers have pointed out the importance of studying group interactions within focus groups. However, most researchers used a qualitative approach and mostly explored the interaction between participants or between participants and the moderator. This study claimed there might be a third and unobservable interaction that occurs between participants and structured discussion topics. An affiliation network in social network analysis was applied to investigate this phenomenon among eight groups of existing focus group conversations. By affiliation network data and network visualization, this study demonstrated diverse structures between groups. The interaction between participants and discussion topics was significantly different between at least two groups. The results showed that social network analysis could be a tool to help examine focus group interactions from qualitative data, and the interaction between participants and discussion topics could be a potential third interaction in focus group studies. This study is limited by comparing the mean difference between groups. Future research may examine short- and long-term causal effects of group interaction on participation or attitude changes after focus group discussions.