The deadly H5N1 strain of avian flu was found in 28 chickens at a private poultry farm in Bago, about 80 kilometres (50 miles) north of Yangon, in early June, the official said.
The latest outbreak was confirmed on June 7, said Than Hla, an official from the livestock breeding and veterinary department. It was the first bird flu outbreak in Myanmar since late March.
Myanmar has not reported any human cases of bird flu, and Than Hla said there were no reports of human infection.
Following the latest outbreak, authorities killed about 1,000 chickens at the farm. Than Hla said there were three suspected bird flu cases, but officials were still waiting for confirmation from test results.
"It's hard to say when we can declare Myanmar as a bird flu free nation. We are taking preventive measures in the areas hit by bird flu," he said.
Worldwide, the virus has killed 190 people, according to the World Health Organisation. Experts fear the death toll would rise sharply if the virus were to mutate and become easily transmitted between humans.