Support for the AfD dropped one percentage point to 19% in the Forsa poll. It remained in firm second place behind the main opposition conservatives with 32%, while Chancellor Olaf Scholz's centre-left Social Democrats polled third at 15%.
According to the poll, German voters identified ongoing mass demonstrations against the far-right as the most important issue.
The countrywide protests against the AfD have been gaining momentum in the wake of a news report that two senior party members had joined a meeting discussing plans for the mass deportation of citizens of foreign origin. The AfD has denied that the proposal represented party policy.
Following the report, German companies and their CEOs also stepped up warnings about the threat of right-wing extremism to Europe's largest economy.
"All of us as a society, but also the economy and we as companies, must stand up for our values and take up responsibility," Hildegard Mueller, president of the German auto association VDA, said in her opening address to the association's annual conference on Tuesday.
"They also scare off international skilled workers and investors," she added, saying the popularity of such a party would damage Germany's reputation as an export nation.
The AfD, founded 11 years ago, placed first in recent polls in all three eastern German states holding elections this year.
(Reporting by Sarah Marsh and Victoria Waldersee, Writing by Nette Nöstlinger)
