Security in mobile ad hoc networks (MANETs) is an active research topic. Bulks of prior work focused on key management and secure routing without addressing an important pre-requisite: network access control, the problem of how securely extend the network. In this paper, we present INAC, an identity-based network access control scheme for MANETs. In INAC, each node in the network must have an identity-based membership token in order to take part in network activities. Membership tokens have special formats, which not only guarantee security of non-compromised nodes, but also enable that nodes obtain identity-based membership tokens based on their trustworthiness. Through simulations we verify the feasibility of our design in the single authority MANETs.