Johnson's 24-hour Aspire channel targets the African-American community and will include film, TV, music, comedy, performing arts and shows about faith.
It will also offer opportunities for blacks struggling to find work in Hollywood.
Johnson says he's wanted a vehicle to showcase positive images of blacks with stories written, produced and directed by them. His channel will launch in June.
Another network announced on Tuesday, Revolt, was conceived by music mogul Sean "P. Diddy" Combs and MTV veteran Andy Schuon. It will have programming that includes music videos, live performances, music news and interviews.
"Revolt is the first channel created entirely from the ground up in this new era of social media," said Combs, who described the channel as "immediate, like today's social networks."
Revolt is scheduled to launch in 2013.
The other two networks are El Rey, proposed by Hollywood director Robert Rodriguez and FactoryMade Ventures executives John Fogelman and Cristina Patwa, and BabyFirst Americas, from Spanish-language TV veteran Constantino "Said" Schwarz.
These four networks, and the six others yet to be announced, are being chosen from more than 100 proposals, Comcast said. Each will be added as part of Comcast's digital basic tier of service.
The new channels, which in all will total 10 rolling out in the next eight years, are part of an agreement reached by Comcast with the FCC and Department of Justice when it was allowed to become majority owner of NBCUniversal.
The Associated Press contributed to this report.