The 60-year-old has been part of the far-right Sweden Democrats' inner circle since 2005. He was the head of the party's Political Action Committee, as well as the party's treasurer and the chief of economy.
Björklund has now left all his party positions with immediate effect, reports the Nyheter 24 news site.
"He is leaving for health reasons," party spokesperson Martin Kinnunen told the Aftonbladet newspaper.
Björklund denied rumours that he had been forced out of the party with Kinnunen also insisting that it was Björklund's own decision to leave.
The Sweden Democrats refused to go into any detail regarding Björklund's condition.
"We do not comment on colleagues' health," said Kinnunen to the paper.
"This is something we are dealing with internally. He is still employed by the party and we have a responsibility as employers to help members of staff with health issues."
Björklund's tasks and political assignments will be taken over by others within the party.
The Local/nr Follow The Local on Twitter