Like every other question it depends – how long we do it for and the type of chair and it depends on who we are. In truth doing any one thing for too long is not good for our bodies 

The truth is that we need to keep moving – sit for a while and stand for a while is the best way to spend our day so that we don’t overload our joints and muscles.
One study found that in the workplace, productivity increased when people have the ability to sit and stand throughout the work day.

The study, conducted by researchers, examined the productivity of two groups of call-center employees, about 170 employees total, over the course of six months. One group was seated throughout the day, the other group stood up if they wanted to. By the end of the study, the employees using stand-capable workstations were about 46% more productive than the sit-only group (productivity was defined as the number of successful calls each employee completed per hour of work).
The difference in productivity between the groups was significant, but the amount of time spent sitting versus standing was less than first thought. On average, the group who could stand or sit to work actually sat for just 1.6 hours less per day than the sit-only group.

Second, the differences in productivity only started emerging after a full month of the study. It took that long for the participants to adapt to standing part of the day and figuring out what worked best. No one made overnight changes.

The researchers say they also gathered data on employee discomfort and found that “nearly 75% of those working in standing mode experienced decreased body discomfort after using these desks for the six-month duration of the study.” Which also goes to the point that it takes some time to adapt to a combination of sitting and standing, and no one should go into this thinking they’ll magically adapt immediately.
Each position has its advantages and disadvantages. Research indicates that long term sitting or standing are risk factors and that alternating work postures may be preferable. Alternation between two postures allows for increased rest intervals of specific body parts, and reduced potential for risk factors commonly associated with MSD development.
Ideally, provide workers with a workstation and job tasks that allow frequent changes of working posture, including sitting, standing, and walking. If either sitting or standing is feasible but only one possible, sitting in a properly designed chair is preferable.