Officials at India's National AIDS Control Organisation, which is due to launch an ambitious $2.8 billion anti-AIDS plan on Friday, refused to comment immediately on the new figure.
But activists said they were concerned about the lower estimate, especially in a country where over 40 percent of the women have not heard of AIDS.
"A lower estimate may reduce the political will to fight the virus and people may start taking the threat of AIDS lightly. This is a danger," said Christy Abraham, the Indian team leader for HIV/AIDS at voluntary group ActionAid International.
The 5.7 million figure gave India an HIV prevalence rate of 0.9 percent, but on the basis of the new survey this would fall to around 0.3 percent, officials say.
Even the higher rate is far behind South Africa's infection rate estimated at 12 percent. In Botswana, more than a third of the population are thought to be HIV-positive.