Zeynal Bagirzade, who is in the Azerbaijan Popular Front Party's (AXCP) Naxcivan branch, was ordered on December 26 to be held by police in pretrial detention.
Yasar Bagirsoy, Bagirzade's brother and the head of the AXCP's Naxcivan branch, told RFE/RL that Bagirzade was charged with abuse of authority, using false documents, and inflicting great financial damage.
If found guilty of those charges, he could be imprisoned for between one and 12 years.
Bagirsoy said his brother was an invalid who participated in the cleanup of the 1986 Chornobyl disaster and has received a disability pension since shortly after the catastrophe.
"Now they say Zeynal did not ever go to Chornobyl, that he obtained a false document and has been embezzling state resources" because he is not truly disabled, he said.
Bagirsoy said his brother had been active in politics in recent years and aided in establishing the Naxcivan branch of the opposition movement known as the Public Chamber.
"My brother has received this pension for many years. If his documents were false, why have they only noticed now?" he said.
Naxcivan is an Azerbaijani exclave bordered by Iran on the west and Armenia on the east.
Read more in Azeri here