Ghoncheh Ghavami, a 25-year-old law graduate from London, who was detained in June at a Tehran stadium where Iran's national volleyball team was to play Italy, went on trial last month.
"According to the verdict she was sentenced to one year," her lawyer Alizadeh Tabatabaie was quoted in Iranian media as saying, noting that the judge had shown him the sentence.
But no reason was given for the conviction.
Iranian officials have said Ghavami was detained for security reasons unrelated to the volleyball match. So far she has been held in the capital's notorious Evin Prison for 126 days.
The "Free Ghoncheh Ghavami" Facebook page where her friends and family campaigned for her release features photographs of her against the slogan: "Jailed for wanting to watch a volleyball match".
Ghavami's arrest came after female fans and even women journalists were told they would not be allowed to attend the volleyball match at Azadi ("Freedom" in Persian) stadium in the capital.
National police chief General Esmail Ahmadi Moghaddam said it was "not yet in the public interest" for men and women to attend such events together. "The police are applying the law," he said at the time.
