"She's [doing] great," Shelton said of Stefani. "She's sad that The Voice is over, she loves doing the show."
When Kotb joked she doesn't care about The Voice and was wondering how Stefani was doing with him, Shelton adorably replied, "Well, I hope she's good with me!"
"I'm real good with her," he revealed. "We're just content and happy and it's just -- it's an incredible feeling."
The "A Guy With a Girl" singer added that on a typical day when there's no tapings of The Voice, appearances, concerts, etc., he and the No Doubt rocker like to simply sit back and relax.
"Our hobby is just hanging out together, you know?" he explained. "She's my best friend."
Shelton, 40, is up for Male Video of the Year for his "Came Here to Forget" music video at the CMT Music Awards, competing in the category against Eric Church, Jason Aldean, Keith Urban, Luke Bryan and Thomas Rhett. He'll also be taking the stage to perform.
"I'm just glad to get a performance," he admitted, when asked if he was nervous. "An old guy like me, at one of these awards shows? I can't even believe they let me here."
The CMT Music Awards air live from Nashville on Wednesday at 8 p.m. ET on CMT.