The incident happened at the Minneapolis-St. Paul International Airport on Saturday local time and was caught on CCTV.
Delta Air Lines staff immediately tried to reach the boy but were unable to stop him, the airport told Good Morning America in a statement.
The conveyor belt was shut down “within seconds” but the boy then jumped onto another conveyor belt.
Security footage shows the boy sitting on the belt and being carried through a small tunnel that leads to a baggage sorting area.
Police were able to find the boy within four minutes and return him to his parents, the airport said.
The airport is now investigating the incident and said it would work with Delta Airlines to prevent any other similar incidents happening again.
In July last year, a two-year-old boy ended up with a broken arm after sneaking onto a conveyor belt at the Hartsfield-Jackson Atlanta International Airport.
The boy’s mother told ABC News she had put her son down to print out a boarding pass when he took off.