The price of the most popular health plans sold through Maryland’s insurance exchange will jump, on average, by about one quarter next year, fueling questions about whether coverage under the Affordable Care Act will remain affordable in the state and elsewhere.

The 26 percent average increase in monthly premiums are for CareFirst plans, which cover three-fourths of the state residents who have bought insurance under the federal health-care law. The price jump, scheduled for January, is among rate changes that the state’s insurance regulators have approved for plans sold to individual families and small businesses.