The center was visibly upset with Bednar after Calgary scored an empty-net goal with 10 seconds left in the third period to secure a 5-3 victory.
"I can't be doing that stuff. Just frustrated," MacKinnon said after practice at Bell Centre on Friday in preparation for the Avalanche's game at the Montreal Canadiens on Saturday (7 p.m. ET; SN, TVAS, ALT, NHL.TV). "I think we've lost eight of nine and I think [Flames forward Matthew] Tkachuk just scored the empty-netter and I was just really frustrated. I love playing for [Bednar]. Everyone loves playing for [Bednar] in here, and that's on me and I take responsibility for it."
The Avalanche (20-16-8) hold the first wild card into the Stanley Cup Playoffs from the Western Conference but are 1-6-2 in their past nine games and have allowed at least five goals in three of their past four games.
MacKinnon, who at one point slammed his water bottle on the bench, said he was upset with Bednar's decision in the closing minute of the loss to Calgary.
"I just thought the goalie ( Semyon Varlamov ) should have been pulled [sooner] and he didn't," MacKinnon said. "That's all it was. It was just stupid. I was just taking my frustration out on that. I mean, it's just about the goalie being pulled, that's it.
"I think everyone was frustrated, I was just the only one who did that. So no excuses. Everyone wants to win as bad as I do in this room, but they obviously channeled it better than I did. And I definitely can't be losing my temper and treating the coach like that."