The incident took place against Benafsha Girls High School in Tosak village on the outskirts of Farah city.
The school was set ablaze by some armed men last year but it continued to provide education for almost 500 girls.
The officials said the armed men entered the school and placed explosives inside the building and detonated it afterward.
The incident took place against Benafsha Girls High School in Tosak village on the outskirts of Farah city, said Dadullah Qaane, member of Farah Provincial Council.
At least 500 girls are enrolled in the school, he said, adding that the school had received threats many times.
No group has claimed responsibility for the attack.
Statistics by the Ministry of Education show that 3.5 million children are deprived of education and at least 900 schools have remained closed across the country.