Cameroon says widespread corruption in its finance ministry has cost it 1bn CFA francs ($2m; £1m) a month.
The government is checking payrolls at other ministeries
About 500 officials are accused of either awarding themselves extra money or claiming salaries for "non-existent" workers.
Prime Minister Ephraim Inoni, who vowed to tackle corruption when he came to office last year, said those found guilty would face tough punishments.
The scam is believed to have begun in 1994.
The prime minister's office said the alleged fraud was uncovered during an investigation into the payroll at the ministry.
In certain cases, staff are said to have lied about their rank and delayed their retirement in order to boost their earnings.
The prime minister's office said auditors had found "irregularities in the career structure of certain civil servants".
It added that the staff in question "appear to have received unearned salaries, boosting the payroll".
Fidelis Nanga, a journalist based in the Cameroon capital Yaounde, said the government was considering taking criminal action against those found guilty and forcing them to repay any money owed.
"The prime minister has given instructions for exemplary penalties to be meted out against the accused and their accomplices if found guilty," he told the BBC's Network Africa programme.
Mr Inoni launched an anti-corruption drive in December after foreign investors criticised a lack of transparency in the country's public finances.
In one initiative designed to improve efficiency, civil servants who arrived late for work were locked out of their offices.
The government now intends to carry out an audit of payrolls at all other government ministries.
In a report compiled by anti-corruption body Transparency International in 2003, graft was said to be "pervasive" in Cameroon.