My iMac says I have unread messages?

Hi Tomae23,

For help with reading unread messages or clearing the alerts have you tried closing the Message app? If not, test the steps below found in the guide here: Quit apps on Mac - Apple Support

"Quit an app

While in the app, choose App Name > Quit App in the menu bar. For example, choose Mail > Quit Mail.

Note: When you click the red close button  in the top-left corner of an app’s window, the window closes, but the app remains open. See Manage windows."

If the issue continues, let us know if you use Messages on any other devices like an iPhone or iPad and if the unread messages show there. Also, confirm any other steps you've tried. For example, a normal restart of your Mac.

Cheers.