Attacks on the site and protests by residents and the far-right National Democratic Party (NPD) have dogged the mosque's construction.
The demonstrators, many of them older people, held banners reading "Stop the Islamization of Europe" and "Stop the Abuse of Religious Freedom", Reuters reported.
A few black-clad young men with shaved heads, a trademark right-wing style, joined the protest but the NPD called off a march.
The 1.6 million-euro (2.15 million-dollar) mosque has a 12-meter (39-foot) high minaret and can hold up to 500 worshippers -- far larger than
The building of mosques and minarets has sparked controversy in
The protest highlighted difficulties in integrating
Supporters say the mosque will foster better ties.
"The mosque will be a hub of social activity, not just for praying," said Ijaz Ahmad, spokeswoman for the Ahmadiyah mosque.
"It will play a role in boosting integration and promoting dialogue with politicians and other religious groups."
The local citizens' group said Ahmadiyah is a sect with racist and discriminatory views.
"We have a big problem with sects that put religion above everything else, allow the beating of women and deny equal rights," the group said on its website. "Our opposition is directed at this sect's ideas and in particular its ideas about women," it said.
The edifice symbolizes "religious and cultural tolerance in our town,"
The Ahmadiyah movement, whose slogan is "Love for all, hatred for no one", was founded in