The helicopter went down south of Spain's base at Herat on Tuesday, a Spanish Defence Ministry spokesman said. The cause was unknown.
In Kabul, an official of the Nato-led force said a helicopter crash in western Afghanistan had killed a number of Nato-led peacekeepers.
Rescue teams had been sent to the crash site near Herat's airport, said Andrea Tolan, a press official for the International Security Assistance Force (ISAF), Afghanistan's Nato-led peacekeeping force.
Tolan said she did not know the type of the aircraft and added it was too early to judge what caused it to come down.
A Spanish Defence Ministry spokesman, when asked if he could rule out hostile fire, said: "We don't want to say right now what the causes could be. The causes are unknown."
"We don't want to say right now what the causes could be. The causes are unknown"
Spanish Defence Ministry
Herat is in the heart of a relatively secure part of Afghanistan, and the Taliban and its allies are less active there than in the eastern and southern parts of the country.
The crash would be the second air disaster for Spanish troops in Afghanistan. In 2003, a plane taking 62 Spanish peacekeepers back from Afghanistan crashed in Turkey, killing all on board.
Taliban fighters shot down a US military helicopter in June in the eastern province of Kunar, killing 16 American soldiers on board.
Eighteen Americans - 15 service personnel and three civilians - also died in a helicopter crash during a dust storm in Ghazni province on 6 April.
The ISAF is made up of more than 8000 soldiers from 36 countries, most of them Nato members.