The lockdown was lifted shortly before noon and the area was cleared.
No flights were affected by the lockdown, officials said.
Police say the lockdown was triggered when an unattended bag was found on the south side of the terminal around 10 a.m. A canine was brought in to investigate and found something which merited extra attention.
The Los Angeles County Sheriff's Department bomb squad was brought in to investigate.
A 400-foot perimeter was closed off around the bag, but passengers had still been cleared to board planes on the north concourse.