Joint actions are increasingly taking place in virtual reality (VR), as social VR and other forms of VR applications have become more prevalent. It has been suggested that when engaging in joint actions in real world, each individual achieves unconscious coordination with the other by automatically activating representations of the other's behavior in their motor system. In particular, the conditions under which such implicit cooperation with others occurs and how it can be facilitated have been investigated by examining the Social Simon Effect (SSE). However, collaborative partners are not always perceived in the same way between the real world and virtual reality. In particular, the visual representation of the avatar is thought to affect the perception of others' presence and actions. This study looked into (1) whether SSE can occur during joint actions of avatars in VR; and (2) how visual representation of the co-actor's avatar affects SSE. Results showed that SSE was induced when the co-actor's avatar was displayed in full-body or was entirely transparent, but it was absent (or weak) when only the two hands were visible.