The film, which stars Jesse Eisenberg and tells the story of Facebook's founding, took in $15.5 million to hold on to the box office crown.
Katherine Heigl's latest movie Life As We Know It came in second with $14.6 million during its debut weekend.
Disney's big-budget Secretariat faltered at third place during its first weekend of release, while Wall Street: Money Never Sleeps fell out of the top five for the first time since its September 24 opening.
New entry My Soul To Take 3D also landed in the top ten.
The US box office top ten in full:
1. (1) The Social Network - $15,500,000
2. (-) Life As We Know It - $14,600,000
3. (-) Secretariat - $12,600,00
4. (2) Legend Of The Guardians: The Owls Of Ga'Hoole - $7,015,000
5. (-) My Soul To Take 3D - $6,900,000
6. (4) The Town - $6,350,000
7. (3) Wall Street: Money Never Sleeps - $4,625,000
8. (5) Easy A - $4,200,000
9. (-) Case 39 - $2,630,000
10. (6) You Again - $2,470,000