Maybe you're signed into iCloud on a device you don't know about!
I think you mean 'two' not 'to' - I assumed you meant you don't have a MBA.
Any workaround to make it disappear?
Change your apple id password.
I wonder if there was a way to track that second MBA...?
It's not a second MBA, it's an iCloud ghost artifact of yours. Did you happen to be running Yosemite Betas or GMs or reinstalled Yosemite?