The bomb targeted the Eidgah Mosque in Kabul where a memorial service was being held for the mother of Taliban spokesman Zabihullah Mujahid, the spokesperson added.
According to top report, no one immediately claimed responsibility for the attack. However, since the Taliban takeover of Afghanistan in mid-August, attacks by Islamic State group militants against them have increased.
The rise has raised the possibility of a wider conflict between the two extremist groups.
As per report, IS maintains a strong presence in the eastern province of Nangarhar and considers the Taliban an enemy.
It has claimed several attacks against them, including several killings in the provincial capital of Jalalabad. Attacks in Kabul have so far been rare.