Federal authorities Tuesday charged a Wilmington man with threatening to burn Boston’s largest mosque and making menacing statements to Muslims on social media.

Patrick Keogan, 44, posted threats to the Facebook page of Roxbury’s Islamic Society of Boston Cultural Center last November, according to an affidavit filed by an FBI special agent with the US Attorney’s Office in Boston. Keogan’s post included an image depicting a mosque in flames with the superimposed words “Burn your local mosque,’’ the affidavit stated. He also wrote “Hello scumbags,’’ beside a smiley face emoji.

Keogan allegedly posted the same image on the Facebook page of the Islamic Society of Northeastern University.

Keogan, who was interviewed by the FBI in December 2015, appeared briefly in US District Court Tuesday. Wearing a gray T-shirt and cargo shorts, he appeared hesitant and soft-spoken, in contrast to his alleged online presence.

He was charged with making a threat over Facebook to injure or intimidate another individual or to unlawfully damage or destroy a building by means of fire. A detention hearing is scheduled for Thursday.

Yusufi Vali, executive director of the Islamic Society of Boston Cultural Center, said it is not uncommon for the Boston mosque to receive hateful messages or threats. But Keogan’s comments raised special alarm because they came the day after the Nov. 13 terrorist attacks in Paris, which left 130 people dead.

The mosque alerted the FBI to the post immediately, Vali said.

Assistant US Attorney Scott Garland said the investigation into Keogan has been ongoing since the mosque reported the threat and that the delayed arrest is simply the result of the “investigative process.’’ Vali said the FBI has been in touch with his organization throughout and that he did not feel endangered in the meantime.

After the hearing, Keogan’s lawyer did not address details of the charges.

Speaking to the FBI in December,Keogan denied that he had any intention of carrying out the threats. “Keogan said that he was sorry and that he needs to smarten up as he is too old to act this way,’’ the affidavit said. “Keogan also said that he does not intend to harm Muslims or commit any damage to mosques.’’

Through a warrant that authorized a search of Keogan’s Facebook account, investigators found several posts expressing support for attacks on mosques, the affidavit said. After an Islamic center in Missouri was reportedly set aflame in 2013, Keogan allegedly praised the unidentified man as “an unknown hero.’’

“The people’s champion. A true God amongst mortal men. May your days be many & troubles be few my good man,’’ he allegedly wrote.

In November 2015, he made a post reading, “Canada enters the Mosque Burning Winter Olympics of 2016 early!’’

After the vandalism of a mosque in Burlington last year, Keogan wrote that he had wanted to disrupt a gathering held in solidarity with the Islamic community there.

In 2013, after allegedly making threats against Congress, Keogan told the FBI he often became vocal about his political beliefs, “especially when drinking,’’ the affidavit said. Keogan said he sometimes “drinks too much.’’

Keogan, who was convicted in 2006 for assault and battery with a deadly weapon, is also accused of illegally possessing ammunition as a felon.

Keogan had allegedly posted photos of himself holding an assault rifle and pictures of other firearms. Investigators also tracked him while he bought ammunition in New Hampshire and drove it back to Wilmington, the affidavit said.

There was a significant increase in threats and vandalism against mosques in 2015, said John Robbins, executive director of the Council on American-Islamic Relations in Massachusetts.

“Unfortunately, when mainstream politicians and local ­anti-Muslim hate groups continue to use tragic acts to demonize large swaths of the Muslim community, it isn’t surprising to see these kinds of reactions,’’ Robbins said.

Vivian Wang can be reached at vivian.wang@globe.com. Andy Rosen can be reached at andrew.rosen@globe.com.