The male victim had 10 bullet holes in his head, chest and stomach, and was discovered in the Mushaki area of Qarabagh district in Ghazni province, said police officer Abdul Rahman.
The grim discovery came hours after a purported spokesman for the group claimed they had killed one of the 23 South Korean nationals taken captive by the group.
Also Wednesday, a group of the abductees - six female and two male - were freed and taken to a U.S. military base, a Western official said.
Purported Taliban spokesman Qari Yousef Ahmadi said militants told him the slain hostage was sick and couldn't walk and was therefore shot.
Some of the 23 Korean hostages, meanwhile, had been freed and were taken to a U.S. base in Ghazni, said two Western officials who asked not to be identified. The officials did not know how many had been freed. The South Korean news agency Yonhap said eight Koreans had been freed, citing unnamed Korean officials.
An Afghan official involved in the negotiations earlier said a large sum of money would be paid to free eight of the hostages. The official spoke on condition he not be identified, citing the sensitivity of the matter, and no other officials would confirm the account.
Foreign governments are suspected to have paid for the release of hostages in Afghanistan in the past but have either kept it quiet or denied it outright.
The South Korean hostages, including 18 women, were kidnapped last Thursday while riding a bus through Ghazni province on the Kabul-Kandahar highway, Afghanistan's main thoroughfare.
In a separate kidnapping case, a German journalist and two Afghans colleagues were kidnapped by Taliban militants in a dangerous and remote area in eastern Afghanistan on Wednesday but were released hours later, said Kunar Gov. Dedar Shalezai.
The spate of recent kidnappings — 26 foreigners have been abducted in the last week — prompted the Afghan government to forbid foreigners living in Kabul from leaving the city without police permission.
Police said officials stationed at checkpoints at the city's main gates would stop foreigners from leaving Kabul unless they informed officials 24 hours in advance of their travel plans, said Esmatullah Dauladzai, Kabul's provincial police chief. The directive, issued Wednesday, is related to the recent kidnappings, he said.