How To Disable Messages In Os X Yosemite Without Disabling It On Your Phone
1
Open Messages
On your computer, navigate to Applications > Messages.app (or use Spotlight).
2
Open the Accounts preferences pane
In the menu bar, Navigate to Messages > Preferences. Then, select the iMessage tab.
3
Disable iMessage
On the Settings tab, uncheck Enable this account.
That’s it!