Investigators don't believe the incident is linked to terrorism and no threat was called into the airport, said Det. Gus Villanueva.
No flights were affected by the explosion, authorities said.
On Sunday night, someone planted a plastic bottle containing dry ice that exploded in an employee bathroom in LAX's Terminal 2.
Up to four flights were delayed after airport police halted security screening for more than an hour.
No arrests have been made in either case.
A bomb squad was at the airport late Monday and investigators from the LAPD's criminal conspiracy division were assisting, Villanueva said.