The aid agency has had no contact with the gunmen, an ICRC spokesman says.
Earlier, Syrian state media said gunmen had opened fire on Red Cross staff travelling on the road between Sarmin and Saraqeb in Idlib province.
The ICRC says it has been struggling to gain access across Syria to provide aid to injured and displaced people, especially in besieged areas.
A convoy carrying six ICRC staff members and one Syrian Arab Red Crescent volunteer was intercepted by unidentified armed gunmen near the town of Saraqeb in Idlib province, ICRC spokeswoman Rima Kamal told the BBC.
"We call for the immediate release of the seven colleagues abducted this morning... who work tirelessly to provide assistance to those most in need in Syria. Incidents such as this one unfortunately will undermine our capacity to assist those who need our help," she said.
The ICRC has declined to reveal the identity, gender or nationality of the abducted workers but they are believed to include both local and international staff, who are mainly medical specialists.
Syrian state news agency Sana earlier quoted an unnamed official as saying the workers were abducted and taken to an unknown location after gunmen blocked their path and shot at their convoy.
Syrian Red Crescent volunteers were on hand to help evacuate some 1,500 people from the besieged Damascus suburb of Muadhamiya this weekend.
Another ICRC spokesman, Simon Schorno, told Associated Press the attack took place at around 11:30 (08:30 GMT) on Sunday as the team was returning to Damascus.
He said the team had been in the field since 10 October to assess the medical situation and deliver aid in what he described as "a difficult area to go in".
It is not yet clear who carried out the kidnapping, but Syrian state TV said "armed terrorists" targeted the convoy.
Kidnappings, particularly of aid workers and journalists, have become increasingly common in the north, where much of the countryside has fallen into militants hands.
In August, the ICRC said the number of Syrian Arab Red Crescent volunteers who had lost their lives since the start of the conflict had risen to 22.
The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following intervention of western and regional states.
According to reports, the Western powers and their regional allies -- especially Qatar, Saudi Arabia, and Turkey -- are supporting the militants operating inside Syria.
SHI/SHI