Afridi had been due to play with Sydney Thunder. Ajmal signed for Adelaide Strikers and Umar for Sydney Sixers but the PCB ordered them to feature in a domestic Twenty20 event being used to test players ahead of the matches against arch-rivals India.
But on Monday, PCB spokesman Nadeem Sarwar said they would be allowed to play in the Big Bash following a request from Cricket Australia that said they had already signed their contracts.
"We will allow these players to go to Australia at the end of our Twenty20 tournament around December 8," Sarwar told AFP, adding that the players will have to return for the national camp for the Indian tour.
Pakistan will play India in two Twenty20 matches and three one-day internationals between December 25 and January 6 -- the two countries' first series since 2007.
All three players were reportedly concerned about not being signed in the future for the Big Bash if they had not honoured their contracts.