Click Energy has announced it will implement a 3.5% increase in household electricity rates, "due to a rise in wholesale and market costs".
It said this would result in the typical annual domestic electricity bill rising by about £39.60. The rates are effective from 1 November.
Click Energy said it recognised that "any increase in energy prices is disappointing and not something customers ever want to hear".
However, it added that it had "not increased its domestic prices in over three years".
"Unfortunately, the sustained rise in wholesale and market costs means it has become necessary for us to adjust our rates accordingly," Andy Porter of Click Energy said.
"At Click Energy, our priority has always been to provide customers with transparent pricing and strong customer support.
"We remain committed to delivering fair value and to helping those who may be struggling with their bills."
Raymond Gormley, head of energy policy at the Consumer Council, said a typical Click Energy credit customer would "see their annual electricity bill increase from around £1,141 to £1,171 and a typical prepayment customer will see their annual costs increase to around £1,181".
"While this is unwelcome news for around 33,000 Click Energy consumers, the main drivers for this are rising wholesale and market related charges," he said.
Mr Gormley said he would encourage consumers "to think about the way they pay for their energy and see if they can reduce their energy costs".
Last month, Power NI said an electricity price tariff rise of 4% was "unavoidable" following a review by the Utility Regulator.
It was the second tariff increase from Power NI in less than a year.
Meanwhile, SSE Airtricity announced that gas prices in Greater Belfast and West would be dropping by 8.47%.
Firmus Energy announced its gas price in the Ten Towns area would fall by almost 8% in October, which is the equivalent to £78 a year for a typical customer.
The Ten Towns area includes Antrim, Armagh, Banbridge, Ballymena, Coleraine, Craigavon, Newry, Lo