The adult 'star' tested positive for the condition at a centre in California's San Fernando Valley, nicknamed Porn Valley for the huge amount of adult titles produced in the area.
The disclosure drew criticism from health campaigners, who described the positive test as 'preventable' because porn stars often have unprotected sex on film.
A clinic in Sherman Oaks, California, frequented by those in the porn industry, confirmed the infection.
We do have a confirmed adult-industry performer who tested positive for HIV,' said Jennifer Miller, a sexually transmitted disease counsellor at the clinic.
'We are quarantining and testing all exposed partners to the individual who tested positive for HIV.'
The clinic did not immediately reveal whether the performer was male or female.
'We're doing what we can to notify the individuals involved,' Miller said.
Two of the areas largest porn producers immediately announced a halt to their porn productions.
Officials with Vivid Entertainment, a porn production company based in Van Nuys, and Wicked Pictures, based in Canoga Park, announced they had immediately ceased filming.
'When Vivid was first made aware that a performer had tested positive for HIV we immediately suspended production,' Steven Hirsch, Vivid's co-founder, said in statement.
'We did this as a precaution and will continue to monitor the situation. AIM Healthcare acted appropriately to quarantine all adult talent who may have been exposed. We will wait for all of the facts to emerge before we resume production.'
An outbreak among performers in 2004 occurred when an HIV-positive male porn star, Darren James, infected three female performers with whom he'd filmed sex scenes.
James, who had worked outside the U.S., was not aware of his positive status at the time he performed.
Dozens of performers who had contact with James and the three women needed additional testing, shutting down production for a month in the spring of 2004.
In light of the infection, the AIDS Healthcare Foundation, which has been leading efforts to change California worker-safety health code, held a press conference this afternoon to address the HIV case.
'That a performer tested positive for HIV today - and that more may be infected - was totally preventable,' said Michael Weinstein, president of AIDS Healthcare Foundation.
'It is also living proof that testing is not adequate protection against HIV/AIDS and other sexually-transmitted diseases among porn performers.'
'How many more people have to be infected with HIV before L.A. County steps in to do its job?'
Last year it was revealed up to 22 performers had contracted the HIV virus, but the U.S. adult industry only admitted to one such case since the 2004 outbreak.
The information was released by the Los Angeles county Department of Public Health
