The university is said to be owing the state government a whooping N1.8 billion under the Pay As You Earn (PAYE) policy.
The main gate of the institution was sealed by the revenue service on Wednesday morning.
Prior to sealing the main gate with padlocks, the OIRS team had shut the institution’s senate chamber and the administrative building.
The money owed by OAU is said to be outstanding unremitted PAYE withholding taxes and developments levy which had become due and payable since 2015 and 2016.
The OIRS had earlier issued a seven-day ultimatum to the institution on the unremitted funds.
The management of OAU has said the debt was inherited from the past administration of the institution.