Officials say Dimeji Bankole was planning to flee the country He was held after a four-hour stand-off at his home in the capital, Abuja.
President Goodluck Jonathan was sworn into office a week ago promising to tackle Nigeria's endemic corruption.
The BBC's Jonah Fisher says Mr Bankole's arrest comes as no great surprise after weeks of speculation in local newspapers that he would be detained.
A spokesman for Nigeria's anti-corruption body, the Economic and Financial Crimes Commission (EFCC), said it had received information that Mr Bankole was planning to flee the country.
Along with all other lawmakers, Mr Bankole's term of office expired on Friday - a new parliament is due to be sworn in on Monday.
He lost his seat in April's elections.
An EFCC statement said Mr Bankole was wanted for questioning over a series of allegations.
They include the misappropriation of $60m (£37m), and the taking out of a $65m (£40m) personal bank loan using parliament's account as collateral.
Mr Bankole's spokesman, Idowu Bakare, has previously issued a statement saying he had "never benefited" from his position, reports the AP news agency.
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