JOIN USThe suspected suicide bomber was also killed when the explosives-packed motorbike he was riding blew up in the southern town of Spin Boldak, the Kandahar province border police chief said.
The explosion also wounded eight civilian passers-by -- including two women and two children, said police chief Jawad Ahmad.
There was no claim of responsibility for the attack but militants allied to the extremist Taliban militia are active in southern Afghanistan and across the border in Pakistan.
The man had pulled up alongside a restaurant in the bus station before the motorbike blew up, Ahmad said.
"Including the suspect, five were killed and eight were wounded," he said.
Spin Boldak, which is near a busy border crossing with Pakistan, has come under regular attack with strikes most often directed at the security forces although more civilians are usually killed.
The Taliban were in government for five years until 2001 when they were toppled in a US-led invasion weeks after the 9/11 attacks on the US, blamed on the Al-Qaeda network which at the time had bases in Afghanistan.