At least 12 of Nigeria's 36 states are said to owe their workers more than $550m in salaries and allowances.
Some workers have not been paid for seven months.
The government revenue, which depends largely on crude oil exports, has fallen sharply in recent months because of a fall in global oil prices.
Last month, Mr Buhari said the treasury was "virtually empty".
He has vowed to recover billions of dollars "stolen" under previous administrations.
The president won elections in March on a promise to tackle corruption, seen as one of the country's biggest problems.
Nigeria is Africa's biggest oil producer but much of the revenue is said to be stolen.
A government statement said the money would come through soft loans from the central bank, and dividends paid by the state-owned natural gas agency.