Trend Micro Security (for Mac) displays agents as inactive:
If you use the agent uninstallation program to remove the agent program from the endpoints but do not unregister the agent from the server.
If you reformatted the endoint hard drive without unregistering the agent from the server.
If you manually removed the agent files.
If a user unloads or disables the agent for an extended period of time.
To have the agent tree display active agents only, configure Trend Micro Security (for Mac) to automatically remove inactive agents from the agent tree.