"The Office" co-stars played love interests on the U.S. comedy series, and even dated in real life for two years until parting ways in 2007.
However, the former couple has remained good friends, and in an interview with Good Housekeeping magazine, Mindy explains she actually asked him to take on a special role in helping to raise little Katherine, who was born in December, 2017.
Their close relationship has repeatedly sparked rumours suggesting the 39-year-old "Ocean's 8" star is secretly dating B.J. again, and although Mindy insists that really isn't true, she can understand why people think they're more than friends.
"If I was on the outside looking at it, I would think the same thing," she said. "But the truth is that B.J. is so much more like family now than a platonic friend. He's the godfather to my daughter, he comes over like once a week. Sometimes he'll come over just to hang out with her."
She now calls Novak "a real staple in my household".
"In the When Harry Met Sally version of platonic friends, I too think that's strange," she explained. "But when you've known someone for as long as I've known him - the time that we met each other, which was like 24. Now, we're both almost 40. It's such a long time that he truly is just a part of my family."
Back in 2015, the the mother-of-one confessed that her relationship with Novak was "weird as hell".
"He is not my boyfriend, but he is not my best friend," she told InStyle. "I guess you could describe our relationship as a 'romantically charged camaraderie with loud arguments,' but I don't think Facebook would accept this as a new status."
Her comments echoed remarks made by Novak in a 2014 chat with People magazine, in which he described the funnywoman and their relationship as "complicated", adding, "But I wouldn't trade it for anything in the world."
In addition to spending time together with Katherine, Mindy and B.J. have also enjoyed nights out as pals - in February, the pair attended the Vanity Fair Oscars viewing party together for the second consecutive year.