Publicly verifiable secret sharing (PVSS) allows not only shareholders themselves but also everyone verify the shares of a secret distributed by a dealer. It has a lot of electronic applications. In this paper, we propose a publicly verifiable member-join protocol for threshold signatures. In our proposal, a new member can join a PVSS scheme to share the secret only with the help of old shareholders. What’s more, everyone besides the new member can verify the validity of the new member’s share, while only the new member knows his share. Different from previous protocols, our protocol can tolerate a mobile adversary. This proposal adapts to many electronic applications. Finally, we analyze the security of our scheme.