If you guys are in a relationship, then yes.
If no, then don't worry about it.
You gotta remember, a best friend is far more than just a friend or acquaintance
For women, a best friend is someone that they confide in when shyt goes left, someone they go on trips with, someone that they feel is integral to their life.
So when you guys fight (which all couples do, it happens), she will go to him for advice.
There will be times when she flies out to meet him or vice versa
etc etc.
Personally I don't "worry" about male best friends because I dont even entertain the idea of seriously dating a woman with a male best friend.
Just like I don't think I would be serious dating material if I was always with a female best friend. I've seen it go left far too many times
However in your situation OP, it sounds like you dont have nearly enough info to make that determination, and you also don't seem to be in an actual relationship so its not really your business yet.