The source, requesting anonymity, told The Anadolu Agency that the 70 people had been arrested in August for taking part in demonstrations marking the first anniversary of the violent dispersal by Egyptian police of two Cairo sit-ins staged in support of ousted President Mohamed Morsi.
He said the 70 were accused of belonging to an illegal group, namely Morsi's Muslim Brotherhood movement, which was designated a "terrorist" organization by the government in December of last year.
The defendants, he added, were also accused of obstructing the work of state institutions and taking part in an unauthorized protest.
In October, President Abdel-Fattah al-Sisi signed a bill into law that refers attacks on state institutions and public facilities to military courts.
The move was widely criticized by local and international rights organizations, which voiced fear that defendants would not receive fair trials before military courts.