He said the mini-gyms would be installed next to computer terminals, so anyone queuing to use the internet can take time for a quick workout.
He said: "This new project will hopefully encourage many more library users to think about getting fit bodies as well as fit minds.
"The gym equipment will be discreetly placed so as not to interfere with the day-to-day running of the library and special clothing will not be required.
"And library users can do as much or as little as they want - if people only want to do a five-minute session, they can do just that."
Instructors from the city's leisure centres will be on hand to show visitors to the library how to use the equipment, and offer advice about building exercise into their daily lives.
They will also promote activities available under Liverpool's "Active City" banner, including Walk for Health, Cycle for Health, Taste for Health and Quit Smoking schemes.
John Marsden of Active City, which encourages Liverpool people to be "More Active, More Often", said: "Busy people often see working out as an indulgence they shouldn't waste time on - or they simply don't enjoy disciplined work-outs.
"It's just a matter of treating your chosen activity as a multi-tasking opportunity."