Moving in synchrony with one another is a fundamental mechanism that maintains human social bonds. Yet, not all individuals are equally likely to coordinate their behaviors with others. The degree of interpersonal coordination is greatly influenced by pre-existing characteristics of the interacting partners, like the cultural homogeneity of a group, shared goals, and the likability of the other person. Considering that most research questions necessitate an experimental set-up without such uncontrolled biases, we created a novel, unbiased paradigm: a human-avatar body sway synchronization paradigm. Participants’ body sway was measured by a force plate while being exposed to a medio-laterally moving avatar. Forty-nine participants were tested in a social condition (motionless vs. moving avatar) and a non-social control condition (motionless vs. moving column). The results revealed that participants increased their body sway on their medio-lateral axis while the avatar was moving. The participants did not increase their body sway in the non-social control condition, indicating that the participant’s movement was not simply caused by a basal motion perception process. The current study builds a methodological fundament that can help to reduce biases due to pre-existing rapport between interaction partners and serves as a valuable experimental paradigm for future synchrony studies.