He was aged 57.
Onukaba died at about 6pm on Sunday at a village near Akure, the Ondo State capital.
The spot is said to be about 10 minutes to Akure.
He was on his way back to Abuja from Abeokuta, Ogun State, where he had joined other dignitaries to attend the inauguration of the Olusegun Obasanjo Presidential Library.
One of his relations, Yusuf Itopa, confirmed his death to the News Agency of Nigeria in Lokoja on Monday.
Itopa said that late veteran journalist turned politician was knocked down by an oncoming vehicle, while running into a nearby bush to escape an armed robbery attack.
Itopa, who is devastated by the death of Onukaba said three of them, including his driver, were traveling when they ran into a blockade mounted by armed robbers.
He said Onukaba’s corpse was later deposited at a mortuary in Akure, from where it will be brought for burial on Monday (today) in his hometown, Ihima in Okehi Local Government Area of Kogi State.
Onukaba, who was Senior Special Assistant on Media to former Vice President Atiku Abubakar, had earlier lost his first wife, Rachael, about five years ago.
He, however, remarried in 2015 to Memunat
Onukaba is survived by three children – two girls and a boy.
He started his journalism career in The Guardian in 1983.