The flights resumed Friday, said Lt. Col. Cathy Abbott, a Pentagon spokeswoman.
Officials hadn't planned on starting the patrols again until next week's 9/11 anniversary, reports CBS News correspondent Jim Stewart. They'll continue indefinitely.
But Stewart says the early resumption may be related to U.S. intelligence and law enforcement agencies detecting increased "chatter" or communications among known al Qaeda operatives.
One senior official described the chatter to Stewart as "terrorist electronic and internet intercepts," some of which are in the form of morale boosting messages such as, "Stay tuned. Good news is on the way."
Much of the increased chatter is taking place in Afghanistan and began to spike in volume earlier this week. It suggests an impending attack against the U.S. or its allies, but contains no specifics, the officials say.
The increased communications are "less intense" than the ones that occurred around July 4, but are intense nonetheless, the officials add.
Some officials speculated to Stewart that the chatter could be related to the Sept. 9 anniversary of the assassination in Afghanistan of a Northern Alliance leader.
Pentagon officials declined to say Friday whether the resumption of air patrols was because of a specific threat or because of the one-year anniversary of the attacks.
But one official told Reuters, "With members of Congress flying to New York, and the anniversary approaching, it was decided that the patrols should resume."
Congress met in New York on Friday for the first time in more than 200 years to mark next week's anniversary of the Sept. 11 attacks.
In addition to the resumption of the 24-hour air patrols, the U.S. embassy in Kabul, Afghanistan has been "buttoned up," Stewart reports.
The Pentagon began the round-the-clock patrols after the Sept. 11 attacks and started phasing them out in April, Pentagon officials have said. The patrols had continued sporadically when officials received threats.
Before the patrols were reduced, they had tied up more than 200 fighter jets and 10,000 Air Force personnel at 30 bases across the country. Air Force officials said they had caused wear and tear on equipment and stress on personnel, costing more than $502 million between last September and January alone.
The resumed patrols involve F-16 fighters and other jets and are being flown by both Air National Guard pilots and regular Air Force personnel.
While officials are concerned that al-Qaida may try an attack on the anniversary of Sept. 11, they note the group has never marked anniversaries or holidays, unlike other terrorist organizations.
Federal law enforcement officials have issued no major terror alerts to local police in recent days, according to a Justice Department official.
In a related development, German authorities said Friday they arrested a Turkish man and his fiancee, a civilian employee of the U.S. military, who are suspected of planning an attack on a U.S. military installation.
The couple had 287 pounds of chemicals and five pipe bombs at the time of their arrest Thursday in an apartment near Heidelberg, where the U.S. Army Europe is headquartered.
"We suspect that they intended to mount a bomb attack against military installations and the city of Heidelberg," the chief law enforcement officer for Baden-Wuerttemberg state, Thomas Schauble told reporters.
The 25-year-old man appeared to be a follower of Osama bin Laden, and was a strict Muslim "who hates Americans and Jews," Schauble said.
His 23-year-old fiancee worked at a supermarket at a U.S. installation in Heidelberg and holds joint German-American citizenship. The man worked at a chemical warehouse in nearby Karlsruhe. They were arrested in their apartment in Walldorf, about six miles south of Heidelberg.
No official has made a connection between the German arrests and the increased chatter within Al Qaeda but the timing is certainly suspicious.