According to OddsShark, the 49ers opened as 5-point favorites over the Ravens. The lines have shifted slightly, with some books making the Niners 3 1/2 point favorites, while others have the Niners as 4-point favorites.
The over/under for the game originally opened at 49, but has since moved to either 47 or 47 1/2 -- depending on the book.
For the Ravens, being an underdog is familiar territory. Baltimore pulled off two major upsets en route to reaching Super Bowl XLVII, defeating the top-seeded Denver Broncos in double overtime during the AFC's Divisional Round, before defeating Tom Brady and the New England Patriots in the AFC Championship game.
San Francisco, meanwhile, was favored on the road in the NFC Championship game against the top-seeded Atlanta Falcons, so it comes as no surprise that they're favored to beat the Ravens.