The company said the outage was resolved Friday night after several hours. It affected registers at 7,000 company-operated stores in the U.S. and 1,000 in Canada.
"All Starbucks stores in the U.S. and Canada are expected to open for business as usual on Saturday," the company said in a statement late Friday night. "We apologize to our customers for this inconvenience. "
The problem began in the early evening Friday on the East Coast and in the late afternoon on the West Coast.
Stores that had not already closed for the evening were closed early, the company said.
Starbucks said the outage was caused by "a failure during a daily system refresh." Company spokesman Jim Olson said that could be called an internal computer system failure but he stressed that it was an internal issue and no external breach was involved.
Earlier, customers found some stores closed and others offered free brewed coffee or tea. In Phoenix, some stores blocked off the entrance to their drive-thrus.
At a Starbucks store in Seattle's South Lake Union neighbourhood, customers were told staff members couldn't process orders. They were, however, being offered coffee at no charge.
"I'm not going to complain about a free cup of coffee," said Suveer Sharma, who was getting a caffeine fix before he headed on a weekend trip to Idaho.
At a Starbucks in Phoenix, customers drove away angrily after seeing closed signs.
"I have a sleeping baby in the back and I'm waiting for a prescription," said Claudia Larson, 40, of Scottsdale. "I wanted a coffee! I'm bummed!"
Starbucks is busiest in the mornings but has been trying to attract more customers later in the day.
In Williamsburg, Virginia, Tom Roberts was part of two couples who stopped by a Starbucks after dinner. He said they accepted the store manager's offer of free coffee or tea.
"They were super polite in coping with it," he said of Starbucks staff.
As in the West, some customers took the news harder than others.
"One guy had been driving all day, he was anxious for a nice fancy Starbucks — but she gave him a large coffee and he was cool," Roberts said. "I think he had a little craving going."
The company said the outage also affected four Evolution Fresh stores and six Teavana Tea Bar stores. Those stores will also reopen Saturday, Starbucks said.
The problem did not affect about 5,000 licensed stores in the U.S. or about 300 licensed stores in Canada, Olson said.
Associated Press writer Traci Carl contributed from Phoenix.