If I reply from my lock screen to a Facebook Messenger message do I go active?

Basically if I reply to message in my notification bar on my IPhone, does my last active stay the same? Or does it update?

You're already active if you're receiving notifications, replying to the message won't change that. If you're getting notifications then Messenger is running in the background which makes your status active. This is why you sometimes see people always active

If its anything like WhatsApp you'd be marked as offline and/or status wouldn't update to state that you were online recently.

You go Active if you Touch Facebook Messenger at all you Become Active