Sydney police say they have been responding to hate crimes aimed at the Muslim community since the Lindt cafe siege in Martin Place.

Barrister and mother of three Katrina Dawson, 38, and Lindt cafe manager Tori Johnson, 34, were killed in the siege, along with 50-year-old gunman Man Haron Monis. Fifteen other hostages survived the ordeal.

Monis's use of a flag with an Islamic creed had prompted fears of reprisals against members of the Muslim community.

At least one man has been charged with making a threatening phone call to a mosque in Auburn on Tuesday as police confirmed a surge in anti-Muslim sentiment.

Police allege a 20-year-old Dural man made a number of threats during the phone call, including threatening to destroy property.

Assistant Police Commissioner Mick Fuller said since the siege there has been some backlash towards the Muslim community.

Sorry, this video has expired Muslim community united in wake of siege

"There has been some issues with hate or bias crimes but it's certainly minimal compared to the outpouring of support and you've all seen the flowers down in Martin Place," he said.

He warned anyone caught up in hate crimes would be prosecuted.

"The New South Wales Police are there to protect anyone and if you break the laws we'll be there to deal with you," Assistant Commissioner Fuller said.

The Australian Muslim Women's Association president, Silma Ihram, said a lot of hate messages have been posted on social media.

"We definitely have seen an increase, as usual, in the postings on social media, in the hate mail that's been coming through to various organisations," she said.

"This is unfortunately what happens every time and the people who they are targeting are completely innocent of anything.

"This is the way that unfortunately people who are extremist in the Australian community take out their anger. They show it.

"That's why that 'I'll ride with you' campaign has been so, so important."

Police have also confirmed the number of people reporting suspicious behaviour or security concerns has risen.

"We've certainly received an increase in information from the community and that's an important partnership and we're dealing with that information quickly," Assistant Commissioner Fuller said.

"There is a large intel cell working at the police operation centre dealing with that information in a timely manner."

The Dural man will face court in January after being released on bail.

He has been charged with threatening to destroy property, using a carriage way to make a hoax threat, using a carriageway to threaten serious harm and using a carriageway to offend.