In comparison to children and young students, adult learners usually exhibit more complex learning behaviors and psychological needs during the learning process. Designing social robots for adult learners has, thus, been a challenging task and a far less explored area, and it requires the great efforts from both technical and theoretical perspectives. We, therefore, first propose a novel framework that exploits the latest artificial intelligence (AI) technologies and the established psychological theory for social robot design. Under the proposed framework, we implement a novel social robot and deploy it in the challenging learning context, which demands the robot provide natural interactions and autonomous learning supports to adult learners. The evaluation results show that the robot significantly improves the learners' intrinsic motivation, and the adult learners have also shown great interests in learning and communicating with the robot. This article sheds light on how to design interactive and autonomous social robots for adult learners and contributes a concrete solution that employs the established psychological theories as the design guidelines and the AI models as the enabling technologies.