The office will be headed by Nunu Ntshingila, a former executive at the advertising agency Ogilvy.
"This office will support the significant growth in businesses and people using Facebook," said a statement from the world's biggest social network, which has some 1.4 billion active users worldwide including 120 million in Africa.
"We are inspired by the incredible ways people and businesses in Africa use Facebook to connect," said Nicola Mendelsohn, regional vice president for Facebook.
Facebook said more than 80 per cent of people in African access the social network from their mobile phones.
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"Mobile is not a trend; it's the fastest development in communications we've ever seen," Mendelsohn said.
"This couldn't be more true in Africa -- where so many people are mobile-only. This new office is a significant milestone for Facebook and our teams want to partner with businesses across the continent."
"Facebook will partner with governments, telecom operators, agencies and other stakeholders to deliver localized solutions to advertisers and users continent-wide," the statement said.