ASIO boss Duncan Lewis says work by foreign intelligence agents that may appear relatively harmless can have significant consequences.

"Hostile intelligence activity poses a real and potential existential threat to Australian security and sovereignty," Mr Lewis told a Senate estimates hearing in Canberra on Monday.

"The harm from this threat may not manifest for many years, even decades, after the activities occur."

The ASIO boss refused to name countries conducting foreign interference in Australia.

"We are concerned about threats from wherever they emanate," he said.

Mr Lewis was also quizzed by Labor and crossbench senators about the recent urgency around passing foreign interference laws, given ASIO said there was no evidence of such activity before the next federal election.

"We have no evidence to suggest there has been or is foreign interference afoot in the electoral process," he told the committee.

"But having said that we are ever vigilant to this matter, it is a live issue, and we are monitoring things very carefully."

Mr Lewis also told the committee the threat of terrorism has "plateaued at a high level" in Australia.

"We can very easily becoming numb to the height of the level because it has become kind of the norm," he said.

Mr Lewis said the twin challenges of terrorism and foreign interference were compounded by rapid advancements in technology.

"Those technologies of course assist adversaries and conceal their activities," he told the committee.

"They also uncover our efforts to discover wrongdoing."

Mr Lewis again stressed the need for parliament to support government legislation giving law enforcement agencies easier access to encrypted information.

"There is no doubt that legislative reform is critical to maintaining our currency of tools to combat the threats posed by those who wish us harm," the ASIO chief said.

Australian Associated Press