Antiretroviral drugs were reportedly administered to the baby in California just four hours after birth.
The unidentified nine-month-old child is now said to be HIV negative.
It is the second such case after an HIV-positive Mississippi infant brought into remission following early treatment was reported in 2013.
"This is a call to action for us to mobilize and be able to learn from these cases," Johns Hopkins University paediatrics specialist Dr Deborah Persaud said at a Boston medical conference.
No trace of the virus can now be found in the infant's blood or tissues, the doctor revealed.
Dr Persaud said the nine-month-old child is still receiving a three-drug anti-Aids cocktail, while the three-year-old Mississippi child stopped receiving antiretroviral treatments two years ago.
"Really the only way we can prove that we have accomplished remission in these kids is by taking them off treatment and that's not without risk," Dr Persaud added.
Both children are reported to have been born to mothers infected with HIV, which weakens the body's immune system.
The human immunodeficiency virus has infected more than 34 million people worldwide, researchers estimate.
US researchers have revealed another baby carrying the HIV virus, which leads to Aids, may have been cured through early treatment.