Is this common, and nothing to bother with? I was in Mantis Labs ( Puce Moose ) converting amps x volts = watts when I saw this message. Dogmeat was nowhere inside the lab to my knowledge, nor did I ever speak to him in the Junkyard.

Did you visit the Scrapyard? If you did, and got close enough to Dogmeat (didn't have to see him) the game sometimes "marks" Dogmeat as active even if he isn't with you. Since he isn't with you he can't die. So you will get that message when he should be killed. Also, he will sometimes leave the Scrapyard and travel. Don't be surprised if you go back to the yard and he isn't there. I have seen him all over the Wasteland from one end to the other.

when you get to scrapyard the first time some raiders attack dogmeat.after killing them he starts wandering off unless youre near him.if you walked near scrapyard but walked right by without going near him hes probably wandering the wasteland getting into fights.if it continues it may be worth finding him and if you dont want him kill him or leave him somewhere safe.