"During the cruise, the pilot fell asleep, resulting in the aircraft overflying King Island by 46 kilometres," the ATSB said in a brief statement.
Fortunately, the pilot was the only person on board the plane, making a 240km trip during the early hours.
He flew his Piper PA-31 aircraft past its destination to King Island by almost 50 km.
Officials at Vortex Air, which owns the plane, have not commented as to how he woke up on time and landed the plane safely, but promised to interview the pilot and review operating procedures.
According to aviation experts, Australia has very strict rules when it comes to pilots working under fatigue.
The last incident involving a pilot error in Australia took place last year when 5 people were killed in a crash in Melbourne.