The man published an advert last autumn in the local Borås Tidning daily on the boy's birthday and in the text of the advert he claimed to be his father.
The man is reported to believe that he is the child's father and despite having taking several tests which prove the opposite, he remains convinced.
The man is known to the police after he made several phone calls to the boy informing him of his conviction.
"It is respectless towards the boy," court prosecutor Kajsa Sundgren told the newspaper.
The boy is reported to have been scared and uneasy at the man's unwanted attention.
The 64-year-old has now been charged with harassment and the boy is demanding 5,000 kronor ($775) in compensation.
The man has acknowledged the chain of events, but denies having harassed anyone.