How to stop my texts (iMessage) from showing on my Mac
Disable it in iMessages Prefs/Accounts...

[Edit] Re-reading your question, you want to be able to send from iPhone &amp; MacBook, but not have the MacBook show any conversations initiated from the phone?
Never tried that one, but perhaps by disabling one or more of the account number/email address options further down the same page.

I've always had conversations appear in both locations, Mac &amp; phone, never seen it behave any differently, unless I was in some poor reception area.