The dispute between candidates Ashraf Ghani and Abdullah Abdullah over alleged fraud in the June 14 election has triggered bitter Internet exchanges between rival supporters that threaten to spill into violence.
Ghani attracts much of his support from the Pashtun tribes of the south and east, while Abdullahs loyalists are Tajiks and other northern Afghan groups echoing the ethnic divisions of the bloody 1992-1996 civil war.
The national security council discussed banning of Facebook in their meeting on Sunday, Fayeq Wahedi, deputy presidential spokesman, said.
There are people on Facebook who spread hatred and cause
damage to national unity, but after talks the council decided not to ban Facebook.
Internet use has rocketed in Afghanistan in recent years, and supporters of both sides have been posting hostile messages and photographs since the fraud allegations erupted.
Two weeks ago, the United Nations issued a warning that the Internet activity could spark civil unrest.
There has been a disturbing tone in some social media platforms, and we urge supporters... to refrain from inflammatory statements, hate speech or statements which promote divisive ethnic mobilisation, UN mission chief Jan Kubis said.