MI5 chief Jonathan Evans will brief MPs as part of their inquiry into the government's counter-terror proposals.
MPs will have an informal briefing with the MI5 director-general
The Home Affairs select committee is studying ideas including extending the time a terrorist suspect can be held without charge beyond 28 days.
The MI5 director-general is expected to say the security service will not make any recommendation on the issue as it does not have power to arrest suspects.
He is likely to outline the nature and evolution of the terrorism threat.
The meeting is an informal private briefing rather than a formal session for giving evidence.
Prime Minister Gordon Brown is attempting to win a cross-party consensus for extending the 28-day limit, which is currently opposed by both the Conservatives and the Liberal Democrats.
Last week, Mr Brown also announced plans to step up security at railway stations, airports and ports as part of government attempts to tackle terrorism.
From next year there will be new security barriers, vehicle exclusion zones and blast resistant buildings, and rail travellers face having their luggage screened at large stations.
Mr Brown said improved security would be brought in at 250 railway stations, plus airports, ports and more than 100 other sensitive locations.
Guidance on how to keep people safe would be sent to thousands of cinemas, theatres, restaurants, hotels, sporting venues and commercial centres, and all hospitals, schools and places of worship.
Architects would be encourage to design better security in new buildings, such as blast-resistant materials, safe areas and traffic control measures.
The proposals followed a review by Security Minister Lord West.