Mobile peer-to-peer groups, which do not require any pre-deployed infrastructure or trusted centralized authority are valuable for a variety of collaborative applications. This work is focused on how to securely admit new users to such groups. Existing mechanisms based on threshold cryptography require that prospective members collect sufficient number of individual votes from the group prior to obtaining a membership credential. However, this approach does not consider the desirable anonymity of group members towards the admitted or declined users. This paper presents an admission control mechanism in which group members decide collectively and notify prospective members on the outcome of their decision without revealing their identities to prospective members. Keywords-admission control, peer-to-peer groups, privacy