Warren Blake, president of the Jamaica Athletics Administrative Association, said on Saturday he wouldn't disclose a name until the B sample result was known.
"We have not been informed of any positive B test so I am not in a position to confirm the athlete's name," Blake said in the island's capital of Kingston.
Blake, who managed the Jamaican association's anti-doping efforts before becoming president, said he expects the association to provide more information in a few days.
The positive test was apparently returned at the Jamaica Invitational in May. The competition at the island's national stadium was part of the International Association of Athletics Federations' World Challenge events.
Jamaican sprinters had a dominant run at the London Olympics, winning a record haul of 12 medals, surpassing the 11 they won in Beijing in 2008. The island's talent-deep team was led by Usain Bolt, the world's fastest man.