Police detained the pair, only identified as 16-year-old Sanaa and 17-year-old Hajar, in Marrakesh last Thursday, said Omar Arbib, an activist at the Moroccan Association of Human Rights.
"They were caught kissing and hugging on the roof of a house in Hay Mohammadi district," said Arbib.
"Someone photographed them, sent the picture to the family who informed the police" and the two girls were arrested on the same day, he told AFP.
The Moroccan Association of Human Rights has appointed a lawyer to defend the girls who if convicted could be imprisoned for between six months and three years.
But Arbib called for the release of the pair and for the law they are accused of breaking to be abolished.
Morocco, a country of 35 million people torn between religious conservatism and openness to the West, has had several controversial cases concerning homosexuality in recent years.