An audit by the Liberty Consulting Group released this week said the private utility owes its customers a refund because it paid too much for fuel over the past two years.
Dexter said a measure was put in place in 2009 to ensure customers get the best possible fuel prices. He said if that didn't happen, then residents and businesses should be refunded.
"If the audit is correct, then every cent of that surplus that was taken from Nova Scotia ratepayers should be returned to them," Dexter said after a local announcement in Halifax.
"If there is a miscalculation or if there is more than was necessary taken from ratepayers, that money goes directly, and I would say immediately, back to ratepayers."
Rene Gallant, vice-president of regulatory affairs for Nova Scotia Power, said the utility does not accept the findings of the audit.
"We believe we've done everything we can ... to keep costs as low as reasonably possible," said Gallant.
Nova Scotia Power has asked the Nova Scotia Utility and Review Board for a three per cent rate increase for 2013 and 2014.
Gallant said the audit will be debated in September at a public hearing about the proposed hike.
He said if the provincial regulator accepts the U.S.-based consultant's audit, Nova Scotia Power may be forced to lower power bills by about 1.5 per cent.