I am not sure whether you are looking for MAC OSX agent specifically or NAC agent in general.

However, just FYI, NAC agent on PC/MAC OS is just an agent that communicates with the NAC server. All the policies are configured on the NAC manager itself. Depending on what has been configured, the agent responsibility is to perform posture assessment and remediation.

For information on MAC OSX NAC agent specific, here is the URL for your reference:

http://www.cisco.com/en/US/docs/security/nac/appliance/configuration_guide/47/cam/m_webagt.html#wp1529198

Hope that helps.