Irish Life Health has said that 118 policies on one plan were incorrectly charged and it is dealing with these customers.
The health insurance firm said that its Business Plan Hospital Plus policy was incorrectly priced in respect of these customers.
Affected customers are receiving refunds.
The company said the number of customers involved was very small.
Irish Life Health said it was not an unusual situation in the health insurance industry to discover and rectify any errors in policies and if applicable, to issue customers with refunds.
Last year, Irish Life Health entered the market after acquiring Aviva Health and securing full control of GloHealth.