More than 90 mosques across the UK have opened their doors to visitors to allow Muslims to "explain their faith beyond the hostile headlines".
The Muslim Council of Britain said it hoped Sunday's open day would show unity in "a tense time for faith communities".
Three times as many mosques took part this year as last year, it said.
There are about three million Muslims - about 5% of the population - and an estimated 1,750 mosques in the UK.
The mosques involved in the open day included those in London, Birmingham, Manchester, Leeds, Glasgow, Cardiff and Belfast.
The Visit My Mosque Day comes after supporters of the Pegida anti-Islam movement staged a silent march in Birmingham on Saturday.
The BBC's religious affairs correspondent Caroline Wyatt said fewer than 200 people turned up, but the protest was a sign of the fears over Islam that the open day is aimed at addressing.
The number of anti-Muslim attacks in London has risen since the attacks in Paris, with hundreds reported last year.
'There's a lot of ignorance'
By Emma Ailes, at the Islamic Cultural Centre in central London
The golden dome and minaret of the Islamic Cultural Centre form a spectacular landmark, peeking through the trees on the western fringe of Regent's Park.
Passersby may catch a glimpse of the magnificent chandelier that hangs above the mosque's huge prayer room - today they were invited to venture inside for a closer look.
"My kids always talk about the building when we go past on the bus," says lecturer Berit Eis, 42, who's come with husband Paul and their children Soren, five, and Ellen, four.
"We don't practice a religion but we live in a diverse community and I want them to be aware of different religions. The important thing is not belief, but respect."
Jewish father and son David and Joel Greenbury heard about the day through their synagogue, and were intrigued to see afternoon prayers.
"I think there's a lot of ignorance - people tend to not know about other groups," says David. "As part of another minority religion in the UK, I can relate to that."
The centre's director, Dr Ahmed Al-Dubayan, says he hopes the event is a step towards "clearing away the clouds" of misunderstanding about his faith.
The first of which, he says, is the misconception that today is the only day the mosque's doors are open to outsiders.
"Really, they are open every day."
Among visitors at the Regent's Park Mosque open day were practicing Muslim Nadia Fattouki, 21 and her non-Muslim partner Ben Chappell, 26, both students.
Nadia said she had often encountered a lack of understanding about Islam.
"As a female, if I wear a veil, I have to explain that. I have to explain our inter-faith relationship."
Olima Kalam and her friend Aisha Moriarty, who was brought up Christian but converted to Islam about a year ago, both worship at the mosque.
They said they had not encountered any negativity about their faith personally, but it was important for people to have a better understanding.
"Whatever is happening in the media is ignorance. Islam is about peace and happiness," Olima said.
Sajjad Amin, from Manchester's Khizra Mosque, said: "We're promoting understanding and breaking down barriers by allowing other people to see what mosques do on a daily basis.
"It's not a reaction to that [Islamophobia] - mosques have been doing this over the years. If we can increase the number of mosques participating, we can help to break down barriers."
Mehri Niknam, from the Joseph Interfaith Foundation, a joint Muslim-Jewish organisation, said Muslims faced an uphill struggle to overcome the misconceptions about Islam.
"Humans fear what they don't know, and will invent myths filled with terrifying characters," she said, adding that the "bestialities" of the so-called Islamic State and November's Paris attacks had reinforced many people's fears.
It was "possible and achievable" to address this lack of knowledge through education - but the onus was on Muslims to lead the way, she said.
What happens inside a mosque?
There are more than 2.5 million Muslims in the UK and more than 1,500 mosques. The mosque is a place to gather for prayers, to study and to celebrate festivals such as Ramadan. It can also be used to house schools and community centres.
Find out more and explore mosques around the globe with our interactive BBC iWonder guide: Inside the Mosque: What do you need to know?