Nope. ABC, NBC and CBS are mainstream media.
Mainstream media (
MSM) are those
media disseminated via the largest distribution channels, which therefore represent what the majority of media consumers are likely to encounter.
The largest distribution channels are those transmitted over the air, thus the term "mainstream." Mainstream means "available to everyone" which broadcast is. FNC, CNN and MSNBC are all paid cable networks and thus only available to subscribers. That means they are not considered "mainstream media." They are "alternative media."