Affective communication, communicating with emotion, during face-to-face communication is critical for social interaction. Advances in artificial intelligence have made it essential to develop affective human-virtual agent communication. A person's belief during human-virtual agent interaction that the agent is a computer program affects social-cognitive processes. Whether this belief interferes with affective communication is an open question. We hypothesized that the imitation of a positive emotional expression by a virtual agent induces a positive emotion, regardless of the belief. To test this hypothesis, we conducted an fMRI study with 39 healthy volunteers, who were made to believe that a virtual agent was either a person or a computer. They were instructed to smile, and immediately afterwards, the virtual agent displayed a positive, negative, or neutral expression. The participants reported a positive emotion only when their smile was imitated by the agent's positive expression regardless of their belief. This imitation activated the participants' medial prefrontal cortex and precuneus, which are involved in anthropomorphism and contingency, respectively. These results suggest that a positive congruent response by a virtual agent can overcome the effect of believing that the agent is a computer program and thus contribute to achieving affective human-virtual agent communication. Communicating with emotion, i.e., affective communication, plays an important role in inducing empathy and enhancing human bonding 1-3. With advances in artificial intelligence, virtual agents are starting to play an active role in various fields such as information presentation, sales, training, education, and healthcare 4-10. To help induce a positive emotion and thereby enhance social bonding in human-virtual agent interaction, affective communication between people and virtual agents has become important 11. To achieve the affective communication between people and virtual agents, one of the important issues is a person's belief. A person's belief during human-virtual agent interaction that the agent is a computer program, not a human agent, affects social-cognitive processes 12,13. For example, Caruana et al. reported that subjective ratings of an agent as pleasant and cooperative was lower and saccadic reaction time was longer during a joint attention task in the virtual agent condition than those in the human (virtual avatar) condition, with these conditions being regulated by agency manipulation 13. Thus, the person's belief about the agent, "agency belief," is an important aspect of affective communication with virtual agents. As a means to induce a positive emotion in a person interacting with a virtual agent controlled by a computer program, several researchers have proposed having virtual agents imitate human behavior 14-17. Mimicry (automatic imitation 18) of the human partner's behaviors is known to elicit positive emotions in human communication 19. This means that it might be useful to find ways to suppress the effe...