It said an individual not employed by the AU had tried to withdraw the money from its accounts at the Commercial Bank of Ethiopia (CBE) through forged payment orders to various recipients for construction and water drilling works.
"We commend the vigilance and swift action of the CBE staff and our finance department who successfully thwarted the fraudulent attempt resulting in no funds being withdrawn, averting a potential loss and ensuring that the integrity of our financial controls and management remain intact," the AU said in a statement.
The incident took place on April 15 at a CBE branch within the AU's headquarters in the Ethiopian capital Addis Ababa, it said.
Ethiopian security authorities were informed, the AU said, and "prompt action was taken to ensure the person(s) involved were identified and held in line with their investigative procedures."
The AU said while the attempted fraud was "disconcerting" it had highlighted potential vulnerabilities and led to a review of its security measures.
"We are working closely with the Commercial Bank of Ethiopia to reinforce safeguards and implement enhanced protocols to ensure that fraudulent attempts to compromise the finances of the African Union are prevented."
In March, the CBE said it suffered a technical glitch that saw several thousand customers make fraudulent withdrawals to the tune of millions of dollars.
The bank said about $19.5 million was taken while some media reports put the losses as high as $100 million, official figures show.