The weapons were used by military and police in several countries, news agency TT wrote.
"I can confirm that an investigation is ongoing but I do not want to comment further," prosecutor Henrik Söderman told news agency TT.
According to TT, the five men were between 73 to 43 years old. The 73-year-old man is suspected to have committed the crime during 2010 and 2011. But the man denies all involvement in the weapons deals, the man's attorney told TT.
The Swedish military was not involved with the dealings of the five men, according to public prosecutor Henrik Söderman.