He is replacing Alvydas Kunigėlis, who was dismissed on Wednesday upon reaching the age of retirement.
The director of the State Security Department must have four deputies, but currently only three positions are filled.
Mažeika has been working for the State Security Department for 16 years. Since 2004, he has been heading one of the boards at the department.
The State Security Department is headed by Darius Jauniškis. His other two deputies are Kęstutis Budrys and Remigijus Bridikis.