How do I stop Messages from my iPhone 6s from appearing on my Mac?
On your MacBook, open Messages, then go into the menu bar Messages → Preferences → Accounts. Select your account labeled iMessage, and under Settings, either uncheck Enable this account or click Sign Out. You could also uncheck your phone number and every email address under You can be reached for messages at.

This will stop your Mac from being able to both send and receive iMessages. If you had Text Message Forwarding enabled for your Mac, this will stop it also.