The 60-year-old reality star discussed her 29-year-old son's relationship with the model in a segment on Wednesday's episode of the Kyle and Jackie O Show.
"He's doing really, really well," Jenner said of Rob. "He feels much better about himself ... He's been very, very happy lately and I think he's in a really good place. I don't know too much about their relationship."
"I haven't really seen her that much and I don't know her as well as everyone else, but she seems like a really nice girl," Jenner added of Blac Chyna. "I just haven't been around her too much."
Rob and Blac Chyna have been inseparable since they were first linked in January. The model shares a 3-year-old son, King Cairo Stevenson, with her ex-fiancé, Tyga, who is dating Rob's 18-year-old half sister, Kylie Jenner.
Rob turned 29 years old Thursday, March 17, and celebrated his birthday with his family at Nobu restaurant Saturday. Blac Chyna was noticeably missing from the event, which Kylie and Tyga both attended, but celebrated with Rob on two other occasions.
"The whole family sees that it's [Blac Chyna] who brought Rob back," a source told Us Weekly, referencing Rob's recent return to the spotlight. "There's no ill will toward her, but yes, they're cautious because of the Kylie and Tyga situation."
Blac Chyna's best friend, Amber Rose, clashed with the Kardashians last year after criticizing Kylie and Tyga's relationship. The model herself seemed to diss Kylie over her cooking show in an Instagram post in February.