AIB says it has now paid mortgage interest tax relief due to a number of its customers since February.
Around 1,600 mortgage customers were affected when the tax relief payment was not made earlier this year.
The bank said the issue affected customers who pay their mortgage on the last day of the month, which fell on a Saturday in February.
As the next working day was in March the tax payment for the previous month was not made.
AIB initially said it would repay customers gradually over the course of the year, but later said it would address the issue as quickly as possible.
Today the bank said it has now paid the payment and would write to customers impacted by the error.