Demonstrators have rallied in Lagos for three days, demanding action by the government, with many claiming Buhari's absence is unacceptable and harmful for the country.
"We believe the president has become incapacitated and cannot continue in office, so we are calling for the President to either resume (to continue as president) or resign" Adeyanju Deji, founder of the online campaign #ResistOrResign, told Al Jazeera.
Charles, another supporter of the campaign told Al Jazeera: "It's quite unacceptable that the leader of the most populous African nation in the world would leave the country and go sit down in the UK, on account of a health issue that is unknown to Nigerians".
Some have also used the hashtag #ResumeOrResign.
Buhari, 74, has been under growing pressure to disclose his state of health since a series of lengthy trips abroad to seek treatment for an unspecified illness.
He returned from London in early March after nearly two months away, then left Nigeria again on May 7, 2017.
On the other hand a pro-Buhari group called "Coalition for good governance and change initiative" also took to the streets supporting President Buhari carrying banners that read: "Our President is recuperating. Nigeria is moving forward. No cause for alarm."
Buhari was last in Nigeria in May welcoming back 83 Chibok school girls who had been abducted and then released by Boko Haram. He went on to say that he has "absolute confidence the government will continue to run smoothly while I'm away. God bless Nigeria".
In July, the Nigerian President Twitter account tweeted that Buhari "will be back to Nigeria as soon as his doctors give the go-ahead". As of now it's been more than 90 days since he was last in Nigeria.
While outside Nigeria, Buhari has handed power temporarily to vice president Yemi Osinbajo.