Bomb-squad members investigated the crude, quart-size device April 22 after a person on a cigarette break noticed it on the ground near a trash container, CNN reported Friday.
Austin Chief Arson Investigator Aaron Woolverton said another person saw the object on fire and extinguished it with a bucket of water.
Initial tests of the device showed it contained ammonium nitrate, the same substance that sparked a massive explosion about 110 miles north in West, Texas, last month that killed 14 people and injured 200 others, Austin fire Lt. Randy Elmore said.
He called the device "a legit system."
Woolverton said it looked "more amateur," perhaps an experiment. Authorities are not ruling out the possibility the explosive device is tied to a larger plot, CNN said.
"We are on alert," Elmore said.
No one had claimed responsibility for the failed device and no arrests had been made, CNN reported.