Conversational agents (CAs, aka chatbots) for behavioral interventions have great potential to improve patient engagement and provide solutions that can benefit human health. In this study, we examined the potential efficacy of chatbots in assisting with the resolution of specific barriers that people frequently encounter when doing behavioral interventions for the purpose of increasing physical activity (PA). To do this, six common barriers (i.e., things that stand in the way of increasing PA) were targeted (e.g., stress and fatigue), we adopted domain knowledge (i.e., psychological theories and behavioral change techniques) to design six interventions aimed at tackling each of these six barriers. These interventions were then incorporated into consultative conversations, which were subsequently integrated into a chatbot. A user study was conducted on non-clinical samples (n=77) where all participants were presented with three randomly but equally distributed chatbot interventions and a control condition. Each intervention conversation addressed a specific barrier to PA, while the control conversation did not address any barrier. The outcome variables were beliefs in PA engagement, attitudes toward the effectiveness of each intervention to resolve the barrier, and the overall chatbot experience. The results showed a significant increase in beliefs of PA engagement in most intervention groups compared to the control group, and positive attitudes toward the effectiveness of the interventions in reducing their respective barriers to PA, and positive chatbot experience. The results demonstrate that theory-grounded interventions delivered by chatbots can effectively help people overcome specific barriers to PA, thereby increasing their beliefs in PA engagement. These promising findings indicate that chatbot interventions can be an accessible and widely applicable solution for a larger population to promote PA.