Several people have been killed by a suicide bomber. Photo: BBC Online
Another 13 people, including civilians, were wounded in the attack near Kabul university in the west of the city.
The bomber detonated explosives after approaching the bus on foot.
The Taliban said they carried out the attack, which comes two weeks after a run-off vote to find a successor to President Hamid Karzai.
"As a result of a suicide attack this morning on an ANA [Afghan National Army] air force bus in Kabul, eight army officers were martyred and 13 wounded," defence ministry spokesman General Zahir Azimi said in a statement.
Eyewitness Abdul Kabir told Reuters news agency: "I heard a huge explosion, after that I saw smoke and dust covering the area."
Last month, presidential candidate Abdullah Abdullah survived a suicide bomb attack on his convoy in the capital. Six people were killed.
Afghanistan is still awaiting results from the election.
On Tuesday, the Independent Election Commission said provisional results would be delayed for a week amid allegations of voter fraud.
Officials said thousands of polling stations were holding re-counts in provinces where irregularities had been reported.
Both Abdullah, a former foreign minister, and his rival former Finance Minister Ashraf Ghani have made allegations of fraud.
The vote comes during a critical year for Afghanistan. Most foreign troops are due to withdraw from Afghanistan by the end of 2014.
