Research in human–agent interaction increasingly examines how advancements in AI systems, often designed to mimic human-like traits, impact human behavior. This study specifically examines whether the audience effect, which refers to changes in behavior when people know they are being observed, could be used to measure the influence of AI agents on human decisions related to generosity, fairness, and honesty. A between-group study (N=289) was designed, where economic games (Dictator, Ultimatum, and Mind Games) were played in front of one of three agents: a Computer (minimum expected audience effect), an anthropomorphic Robot, or a Human (maximum expected audience effect). Our first objective was to determine if these games can be used to observe and study the audience effect, by comparing interactions with the Computer and Human agents. Our second aim was to assess whether an anthropomorphic social robot could impact decision-making by comparing interactions with the Robot and Computer agents. Results showed no differences in the Ultimatum and Mind Games when comparing the Human and Computer conditions. In contrast, donations to charities in the Dictator Game were more generous in the presence of a Human than a Computer, suggesting that this game can detect the audience effect of an agent. Importantly, however, no difference emerged between the Robot and Computer conditions, indicating that anthropomorphic design features alone are insufficient to trigger an audience effect. These findings identify the Dictator Game with charities as a method for studying social facilitation effects of an agent, while highlighting the limits of anthropomorphism.