The price rise will come into effect on 01 October.
The firm said the increase is due to increases in the costs of producing electricity.
Stephen McCully, Managing Director of Power NI, said: "So much is dependant upon world fuel costs, which are outside our control and which have an effect on the price we pay for wholesale electricity.
"We have not increased our prices since 2013, so it is particularly disappointing for us that we have to do so now. However, as we were able to cut our prices over the last four years, a typical Power NI bill will still be roughly £80 less than it was in 2013.
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"Unfortunately we cannot avoid this increase, but what we can do, is encourage our customers to take up one of our discount offers, which may help offset it."
Chief Executive of the Utility Regulator, Jenny Pyper, said: "After two price decreases in 2015 and 2016, we signalled last year that we expected the unprecedented period of low global wholesale energy costs to end, with the likelihood that consumer prices would increase. Since the last price decrease in April 2016, forward wholesale costs have risen by around 11%.
"Even after this tariff increase, Northern Ireland will continue to have amongst the lowest domestic electricity prices in the UK and RoI. Power NI's average annual domestic bill will be around 22% cheaper than the GB average annual bill and around 30% cheaper than the ROI average annual bill.
"We continuously review all the components that make up Power NI's tariff. Should wholesale energy or other costs decrease, our system of regulation in Northern Ireland allows us to act as soon as possible to ensure that this reduction is reflected in consumer bills."
(CD/LM)
