Arzumanian allegedly used money from a Moscow-based ethnic-Armenian businessman named Levon Markos to support opposition activities in Armenia.
Arzumanian's lawyer told RFE/RL that his client denies any wrongdoing.
Arzumanian is the leader of the Civil Disobedience opposition movement and is closely associated with Armenia's radical opposition bloc, Impeachment.
The accusations came after National Security Service (NSS) officers searched the Yerevan apartments of Arzumanian and former Deputy Defense Minister Vahan Shirkhanian on May 5, reportedly confiscating large amounts of cash.
The National Security Service alleged on May 7 that the money had been sent to Arzumanian and Shirkhanian by Markos, who fled Armenia in 2005 to avoid prosecution on fraud charges.
Arzumanian told RFE/RL that he visited Moscow to attend the April 25 funeral of former Russian President Boris Yeltsin, but said he did not meet with Markos.
"I have known Levon Markos since 1977, but have not seen him in the last several years," Arzumanian said. "[Prime Minister] Serzh Sarkisian considers Levon Markos his No. 1 enemy and is persecuting that man, having already seized his assets by fraudulent means. He is simply trying to extend that animosity to his political opponents in Armenia.... I have not engaged and will not engage in any illegal activity."
Arzumanian served as foreign minister under President Levon Ter-Petrossian in 1996-98 and is an outspoken critic of current President Robert Kocharian’s government.
Leaders of the opposition have condemned the May 7 arrest.