Herasimenia, who in her career won Olympic medals and retired in 2019, has lived in self-imposed exile since autumn 2020 and was not present at the hearing.
The 36-year-old was found guilty on multiple charges, including "calls for sanctions" and other actions "aimed at harming the national security" of Belarus, said the Viasna rights group.
Herasimenia co-founded the Belarusian Sport Solidarity Foundation (BSSF) in the wake of mass protests that erupted in August 2020 against the contested re-election of strongman President Alexander Lukashenko.
The foundation provided financial and legal assistance to athletes targeted by the authorities for their political views.
It also advocated for a boycott of sporting events held in Belarus and called on the International Olympic Committee (IOC) to suspend the ex-Soviet country.
The organisation was labelled as extremist in Belarus.
Herasimenia had auctioned off a gold medal she won at the 2012 World Championships for over $16,000 (£13,000), using the proceeds to support the foundation.
Separately, a court in Minsk sentenced several trade union representatives including Alexander Yaroshuk to prison violating public order, Viasna said.
