The Department of State Services (DSS) has arrested Eyinnaya Abaribe, a Peoples Democratic Party (PDP) senator from Abia state.
An aide of the lawmaker said he was picked up in Abuja on Friday morning.
It is unclear why the lawmaker was arrested but the development took place hours after he spoke on the 2018 budget.
Abaribe, who is chairman of the senate committee on power, steel development and metallurgy, had alleged that N30 billion was smuggled into the power budget.
He said the N30 billion was listed for expansion and re-enforcement of infrastructure in the distribution companies to reduce stranded firms.
“The amount never passed through the senate power committee. Where did such huge sum of N30 billion come from?” he had asked.
“Let the budget office and other relevant bodies conduct self examination. Such self examination will go a long way to clear gray areas.”
Abaribe stood as one of the sureties for Nnamdi Kanu, leader of the Indigenous People of Biafra (IPOB), who regained freedom after 18 months in detention.
Alongside Tochukwu Uchendu and Emmanuel Shallom Ben, Abaribe signed a N100m bond for the bail granted the IPOB leader in April 2017.
Kanu has not been seen in public since September and Abaribe has been under pressure to produce him.
The senator is also a fierce critic of President Muhammadu Buhari. During a senate debate on the president’s declaration of June 12 as Democracy Day, he said December 31 should be declared as “democracy destruction day” because that was the day the Buhari military government ousted ex-President Shehu Shagari in a coup.