Kehrer, 22, earned a move to Parc des Princes this summer after shining as a youngster with Schalke.
He has settled quickly into life in Ligue 1, and is now a part of the Germany squad after making his debut in September.
"Of course, I have got to know [Mbappe] quite differently as a team-mate," he explained to Goal and Spox.
"As a player, he has outstanding ability, but at the same time he is a very down to earth, funny guy in direct contact."
"Neymar is a sociable and nice person. The way he carries himself privately is quite different to how he may come across in the media.
"In the dressing room, we have a very good mood, which has made it really easy for me so far.
"I grew up speaking French thanks to my family, so I did not have any adjustment problems. I was very well integrated into the team, the people and the city. It worked very well, I feel well in Paris."
PSG have made a storming start to the season, winning all nine games so far in Ligue 1.
The Champions League, however, is the crown that has so far eluded the side, and Kehrer recognises that it is the big prize.
"We certainly have the opportunity [to win]. But it is also certain that it will be very, very difficult," he added.
"There are just an unbelievable number of really strong teams here. From the knockout stage onwards, a lot of details will decide who wins the title."