Currently, science is developing rapidly and its influence on society is more significant than ever. This is all the more reason for today’s scientists to interact with the general public. To design effective science communication activities, we must understand scientists’ motivations and barriers to publicly communicating science. In this study, we interviewed 19 early-career scientists who had participated in science cafes in Japan. From these interviews, we identified five factors leading to their reluctance to participate in science cafes: 1) troublesome or time-consuming; 2) pressure to be an appropriate science representative; 3) outside the scope of their work; 4) could not perceive any benefit; and 5) apprehension about dialogue with the public. Among these factors, apprehension about dialogue may be the clearest reflection of the scientists’ underlying feelings about this form of communication and an indicator of more intrinsic barriers to engaging in science cafes.