The ban took effect on March 31, it said.
"We do not believe [this ban] will automatically eradicate circumcision, but surely it will play a role"
Luul Ghebreab, NUEW president
Female circumcision, also called female genital mutilation (FGM), is widespread in the Horn of Africa and involves cutting off the clitoris and other parts of the female genitalia.
There are degrees of severity and many practitioners are untrained and use crude instruments.
"FGM is a deep-rooted culture and it needs a persistent continuous effort [to halt it]," Luul Ghebreab, president of National Union of Eritrean Women, said.
"We do not believe [this ban] will automatically eradicate circumcision, but surely it will play a role."
Up to 140 million women and girls worldwide are estimated to have undergone female circumcision, and UN agencies estimate that another three million a year are subjected to it.
A health survey by Eritrea's government in 2002 found that 62 per cent of circumcised women in the Red Sea state had the procedure done before their first birthday. Less than one per cent had been performed by people with medical training.