Ibrahim's family members also confirmed that he had been arrested and that they had no information on his whereabouts.
Sudanese security agents have arrested a prominent rights activist, Mudawi Ibrahim Adam, as part of an ongoing crackdown on dissent, Amnesty International said on Thursday.
The 58-year-old was taken into custody on Wednesday at the University of Khartoum where he works as a professor of engineering, the rights watchdog said.
"He was arrested by National Intelligence and Security Service agents... and taken to an undisclosed location where he is at a grave risk of torture and other ill-treatment," Amnesty said in a statement.
Ibrahim's family members also confirmed to AFP that he had been arrested and that they had no information on his whereabouts.
"Mudawi's arbitrary arrest underscores the government's desperate attempts to extinguish the last embers of dissent in the country," Amnesty's deputy director for East Africa, Michelle Kagari, said in the statement.
In recent weeks, Sudanese security agents have arrested several opposition leaders and activists in an attempt to crush widespread protests against a government decision to raise fuel prices last month.
The authorities are determined to avoid any repetition of 2013 unrest that was sparked by a similar round of fuel subsidy cuts.
It was suppressed only by a deadly crackdown by security forces that drew international condemnation.
Rights groups say that crackdown left about 200 people dead, while the government put the death toll at less than 100.
Groups of protesters have staged sporadic demonstrations against the latest round of subsidy cuts, but anti-riot policemen have swiftly dispersed them.
Opposition groups and activists had called for a three-day "stay-at-home" strike in November against the rising cost of living and subsidy cuts. The call had met with a mixed response.
Ibrahim, who has worked extensively on human rights causes in Sudan, has been arrested several times before for his work.
His organisation the Sudan Social Development Organisation was shut down by the government in 2009.