The pollster added that the figures were still lower than the ones during 1980-2002 when about 70 percent of French nationals were concerned over the FN's potential impact on democracy.
The poll was conducted on February 23-27 among 1,006 respondents.
The party, established in 1972, sticks to the values of nationalism, anti-immigration policy, protectionist measures in economy and opposes multiculturalism. The FN has long been associated with the name of its former leader Jean-Marie Le Pen known for controversial statements on Nazi gas chambers used to kill people during the World War II and considered as a xenophobe.
According to the polls of the ongoing presidential race, Marine Le Pen is expected to win the first round of the vote. Her presidential program includes provisions that could deny French citizenship to the undocumented immigrants and simplify their deportation. She also suggested to forbid all organizations linked to fundamentalist Islam, closing mosques designated by the country's Interior Ministry as tied to the extremists.