It says people have become "screen slaves" and are often working while commuting or after they get home.
The society said poor posture in these environments could lead to back and neck pain.
Unions said people needed to learn to switch off their devices.
An online survey, of 2,010 office workers by the Society found that nearly two-thirds of those questioned continued working outside office hours.
The organisation said people were topping up their working day with more than two hours of extra screentime, on average, every day.
The data suggested that having too much work and easing pressure during the day were the two main reasons for the extra workload.
The chairwoman of the Chartered Society of Physiotherapy, Dr Helena Johnson, said the findings were of "huge concern".