The airplane was conducting a charter flight between the Polish capital of Warsaw and the Egyptian city of Hurghada, the Bulgarian National Television (BNT) said.
Following the bomb threat, the crew demanded an emergency landing.
The passengers have been taken away from the aircraft and their identity is being established, with the airplane inspected at a safe distance, The Asia Times reported.
Last month, a Russian plane carrying more than 200 passengers from the Egyptian resort of Sharm el-Sheikh crashed in central Sinai killing all those on board.
The Daesh (ISIL) terrorist group, which has a powerful affiliate in the Sinai, claimed to have downed the plane, which was mainly carrying Russian tourists without offering further details.
It said the attack was to avenge Russia’s air campaign against the group in Syria.