Yes, viable Streptococcus mitis was found on the Surveyor 3 camera returned by Apollo 12. This is described in the report Analysis of Surveyor 3 materials and photographs returned by Apollo 12 (25 Mb, 308 pages).
Eleven different sites among the various parts which were returned were swabbed; each was cultured in 3 kinds of bacterial or fungal growth media (p. 241). Only one culture grew, taken from foam between the circuit boards of the camera. That culture was sent to the CDC in Atlanta, who identified it as Strep mitis (p. 243).
A backup copy (called TAT-1) of the same model camera had been held on Earth in a sealed storage container, and then analyzed in the same manner as the Surveyor camera. TAT-1 carried several species of bacteria and fungi, including Bacillus, Aureobasidium, and Aspergillus pulvinus (p. 243). It's therefore reasonable to conclude that the Surveyor camera could have been similarly contaminated during manufacture or testing. It's unlikely to have come from the astronauts, as no bacteria have been found on other Surveyor samples or on moon rocks, and the foam was buried deep inside the camera.
The report notes that Strep mitis occurs in the human respiratory tract, and can be exhaled in droplets. This particular species is coated in mucus which protects it from freeze-drying (lyophilization). The camera was tested in a vacuum chamber prior to launch, and the report implies that this vacuum testing actually helped preserve the bacterium. In fact, this genus was previously known to last for many years in a vacuum:
It has been shown that several Streptococcus species have remained viable for at least 20 years after lyophilization under routine laboratory conditions (ref. 15).
The report concludes:
The available data indicate that Streptococcus mitis was isolated from the foam sample and suggest that the bacterium was deposited in the Surveyor 3 television camera before spacecraft launch. It is suggested that the bacterium may have been provided some protection from its source in the respiratory tract and that lyophilizing conditions to which the camera was subjected before launch and later while it was on the lunar surface may have been instrumental in the apparent survival of this terrestrial microorganism.