MacBook locked or with virus? (Apple.pass@post.com)
It appears that someone did get ahold of your iCloud account and locked your Mac using Find My iPhone. Usually, you will receive an email if an unknown device logs into your iCloud account, so I would check there to see if any suspicious login attempts were made. 

Unfortunately, the only way to unlock your Mac is to know the password that was used to lock it on Find My iPhone. For now, I suggest that you change your iCloud password. You can take your Mac to a local Apple store or Apple Authorized Service Provider, who may be able to unlock your Mac.

My guess is that Apple.pass@post.com is run by some sort of scam service. Looking online, it seems that other people have encountered this attack, and have been asked to pay a ransom to get access to their Mac. I still suggest you take your device to an Apple store and explain your situation before paying the owners of this account.