Scientists are hoping this will eventually help doctors diagnose the disorder earlier.
The study in the journal Current Biology followed more than 100 babies at 6-10 months and again at three years.
Those who went on to develop autism had unusual patterns of brain activity in response to eye contact with another person.
Most children are not given a conclusive diagnosis until after the age of two.
Diagnosing autism at a younger age would enable earlier therapy which some experts believe could help affected children.