The evacuation of thousands of people shortly after the accident in 2011 sharply lowered their exposure to radiation, a draft report concluded.
The World Health Organisation has said local residents have a slightly higher risk of developing certain cancers.
Reactors at the Fukushima nuclear plant were crippled by an earthquake and tsunami that killed some 19,000 people.
It was the world's worst nuclear incident since Chernobyl in 1986.
The findings of the draft report were presented by the UN Scientific Committee on the Effects of Atomic Radiation (Unscear) in the Austrian capital, Vienna.
Committee member Wolfgang Weiss said the decision by the Japanese authorities to evacuate large numbers of people had proved to be the right one.
"If that had not been the case, we might have seen the cancer rates rising and other health problems emerging over the next several decades," he added.
Unscear's report also stated that "no radiation-related deaths have been observed among nearly 25,000 workers involved at the accident site".
Studies after Chernobyl linked cases of thyroid cancer to radioactive iodine that contaminated milk. But Mr Weiss said that had not been the case in Japan.
The report was prepared by 80 scientists from 18 countries and will be published in full later this year.
The findings contradicted a report published by the WHO in February, which said the risk of cancer for those living near the nuclear plant had risen.
Cancer rates are not expected to rise as a result of the Fukushima nuclear disaster in Japan, UN scientists say.