About 123 travelers snagged the low fare, which is as much as 10 times cheaper than similar tickets.
A United spokeswoman didn't say what the regular price of the ticket would be. The airline is notifying customers who booked the fare that the airline will honor the price.
"We're working to fix the problem and to make sure it won't happen again," said spokeswoman Chris Nardella.
This is the second time since May that the United Web site has accidentally kicked out incorrect prices. On May 17, 23 customers found they could fly internationally for less than a dollar.
"Those customers purchased tickets on several different carriers for 25 cents," Nardella said. "It was a decimal-point problem with the system. The tickets were worth about $2,500 and $2,700. We discovered the problem, and also in that case the company honored the fares."
In the latest glitch, Nardella said the company also gave the customers the option to cancel their greatly reduced fares.
Nardella said there have been no takers so far.