Neighbours say undercover officers have been watching the home in the city's southwestern neighbourhood of Charleswood for months.
RCMP took out garbage bags containing what appeared to be computer towers.
It's unknown if Abdurahman has been arrested.
RCMP would only confirm officers executed a search warrant as part of an investigation.
"The large police presence, initially, was to ensure the safety of the officers involved, and the public," Sgt. Bert Paquet wrote in an email. "At this point, any further details could undermine the ongoing investigation."
Abdurahman gained national attention in March when he expressed his extreme views in an interview with a Toronto newspaper.
His father, a career member of Canada's Armed Forces, said CSIS had told him his 23-year-old son was considered a radical extremist.
"They told me he was on the watch list. He was considered a radical extremist and 'we hope he doesn't go to terrorist,'" said the man's father in an exclusive interview with CBC News in March. The CBC is not identifying the father.
"Here you've got your national security force, if you will, monitoring your child," he said. "How would you react to something like that? I didn't know what to say."
The father could not be reached for comment Thursday.
Neither could the homeowner, although she came home mid-afternoon to speak to officers.
'Very pro-Islamic State rhetoric'
Amarnath Amarasingam, a post-doctoral fellow at Dalhousie University, has been researching foreign ISIS fighters and their Canadian family and friends, as part of the Canadian Network for Research on Terrorism, Security and Society (TSAS).
He has been monitoring Abdurahman and hundreds of other Canadian ISIS supporters on Twitter for the past year.
"The son has been quite active online saying things like 'I'm happy to go to jail for something I believe in' or 'I'm happy to continue to do what I do.'
"I think he has been visited by law enforcement and warned by law enforcement and continues to be quite active in terms of posting things that are quite supportive of the Islamic State," Amarasingam said from Waterloo, Ont.
"That kind of very pro-Islamic State rhetoric has been there as well. I think it will be interesting to see if he is charged with something or whether they just took his computers and things like that to search what he has been downloading."
Abdurahman's father has been worried his son would be swept up in new security provisions in Bill C-51. Amarasingam believes that is quite possible.
"This notion that promotion of terrorism can be something you can be charged with. It will be interesting to see if someone like Harun will be the first test case," he said.
"It will be interesting to see how far the government wants to take it and whether he faces any consequences for these kinds of things."
New funding for CSIS
Just today, Prime Minister Stephen Harper announced $136.81 million over five years, and $40.97 million per year following, under his Economic Action Plan 2015 to increase the front-line capacity of the Canadian Security Intelligence Service (CSIS).
The resources will "significantly increase the agency's front-line capacity to combat the growing threat of jihadi terrorism," he said at an event in Toronto.
The money will support counterterrorism capabilities to identify and address threats from those planning acts on Canadian soil or from would-be terrorists trying to travel abroad to commit acts elsewhere.
A CSIS report recently tabled in Parliament identified three ways in which terrorism threatens Canadians:- Terrorists continue to plot direct attacks against Canada and its allies at home and abroad with the aim of causing death and disruption.
- Terrorists seek to conduct activities on Canadian territory that support terrorism globally, including fundraising to support attacks and militant groups.
- Terrorists and their supporters employ social media to reach individuals in Canada for operational purposes and to radicalize them. Some of these radicalized individuals may conduct attacks before travelling abroad or travel overseas to obtain training or to engage in terrorism in other countries. Should they return to Canada, they may pose a threat to national security by attempting to radicalize others, train them in terrorist methods, or conduct terrorist attacks on their own.Suggest a correction