Emotional contagion is the process by which emotions uncon- sciously spread between people, often via emotional mimicry, a process in which we mimic others’ emotional displays, and consequently, converge with their emotions. The social context theory of emotional mimicry in human-human interactions suggests that these processes are modulated by social factors, such as the group membership identities of interactants (whether the interactants belong to the same social group or not). However, the social factors that modulate the emotional contagion between humans and artificial agents are not known yet. Hence, this research attempts to understand the process of emotional contagion in human-agent interaction by conducting an interaction experiment in a competitive in-group/out-group context. Emotional contagion as well as the social attitudes of trust, empathy, liking, bonding, and pro-social orientation were found to be significantly higher in the in-group than in the out-group setting. Furthermore, these social attitudes were highly correlated with emotional contagion, which demonstrates the potential of using emotional contagion as an unobtrusive proxy measurement of people’s social attitudes.