No, there hasn't been any formal declaration from both Nick Cannon and Mariah that suggests they are back as a couple again. Nick and Mariah got married in 2007, and their marriage was blessed with two kids(twins), Monroe and Moroccan. However, both parents separated in 2014, and their marriage officially ended in 2015. Since then, there hasn't been a real move from both parties about whether they still want to be back as a couple again.
Although, Nick once quoted saying if he were to marry anybody again, it would definitely be Mariah. However, Mariah's response to what Nick said wasn't a sweet one. The reason for their separation was not made open to the public, but both Nick and Mariah have always said they ended their marriage because it wasn't growing as it should and that it was the best option which they needed to take, especially for the sake of their children.