A job fair targeting the Nashoba Valley is already oversubscribed by worker-hungry companies in what organizers say is an encouraging sign of an improving economy.

Sixty-one companies have signed up for tables at the Nashoba Valley Job Fair, to be held Friday at the Devens Common Center at Devens, said Sean Rourke, who has been helping organize the event on behalf of state Representative Sheila Harrington, a Republican from Groton.