“He has been fighting for democracy,” said head of BYSHR, Mohammed Al-Maskati, to the Expressen daily.
The man, who has dual-citizenship, was convicted together with eight others to 20 years in prison after allegedly kidnapping a police officer.
He is in his fifties and is a Muslim scholar from central Sweden, according to the Swedish foreign ministry.
The man lived for many years in Sweden but returned to Bahrain in the 2000s after there had been some reforms in the country.
According to Al-Maskati, he has been central in the protests carried out against the regime during the winter and spring.
The Swedish foreign ministry confirmed to daily Dagens Nyheter (DN) that the Swedish embassy in Abu Dhabi has requested to see him but has so far not been granted access.
“One problem is that they don't recognise a dual-citizenship in Bahrain,” Anders Jörle, head of information at the foreign ministry, told DN.
The man has previously been incarcerated for what the regime sees as “oppositional activity” after being arrested in August 2010 when was held isolated without being able to contact his family or lawyer.
He was later released together with some other prisoners in order to appease protesters earlier in the spring.
But when the regime smashed the protest they carried out massive arrests and the man was taken back to jail.
The Swedish man has stood trial in a newly formed military court and according to Al-Maskati they fear he has been undergoing torture.
Human rights organisation Amnesty has criticised the legal procedures in Bahrain where many imprisoned have reported being put through torture.
“We have previously criticised the arrests of this man and other activists.
We have also criticised the terrorist trials. We don't think that the rule of law has been guaranteed,“ said press secretary Elisabeth Löfgren to Expressen.
The man is also set to faces charge of “terrorist activity” with the intention to overthrow the regime in an upcoming trial.
According to Al-Maskati two of the charges could mean the death penalty and several other life imprisonment.
“I fear that he will be condemned to death,” Al-Maskati told Expressen.