Technologies like ChatGPT and other AI tools have impacted learning by giving students more chances to ask questions and explore knowledge. The inclusion of Non-Player Characters (NPCs) as scaffolding in game-based situated learning activities can have a positive impact on learning. The application of ChatGPT to role-playing has potential; therefore, this study designed a "ChatGPT-based NPCs scaffolding Workflow Framework" and used it as the basis for designing and evaluating an educational game for employee ethics training with empirical evidence. This study had 61 participants, divided into a document scaffolding group (n = 32) and a ChatGPT-based NPC group (n = 29) and examined the learning achievement, flow, motivation, and anxiety in the two groups. The results showed that the designs of both groups benefited learning achievement, and both groups could maintain a certain level of high motivation and engagement. Through qualitatively analyzing the content of students' discussions with NPCs, it was found that there is potential for NPC-assisted learning through ChatGPT. Overall, this study explored the efficacy and limitations of using ChatGPT-based NPCs as scaffolding in game-based learning and found that it is extensible. We also present a framework for the design of ChatGPT-based NPCs scaffolding mechanism.