Help with iPod 5 and desktop Mac regarding iMessage The text messages I send through iMessage on my iPod are showing up and notifying my desktop Mac. Is there a way I can stop this
You have to either sign out of your Apple ID on your Mac or disable just iMessage by signing out of it. 

If you use the same Apple ID on both devices, then in general a lot of data will be shared between the devices such a messages, email, contacts, calendar. This is by design to be convenient for people to have access to all their data on all their devices.