Rules, conventions, traditions, and etiquette of men's clothing are made to serve man, man is not made to serve rules. The "rule" that a man should not remove his jacket is for the purpose of preserving a certain standard of decorum in the workplace, as well as symbolically demonstrate a certain seriousness of purpose. If keeping on one's jacket furthers either of those purposes it makes sense. (Depending on one's psychology, keeping a jacket on, even while working alone, may reinforce a serious of purpose.) Disclosure, it is now lunchtime and I am alone in my office, my jacket is off and I have allowed myself to be diverted from work.
On the other hand, if (a), you will not be seeing customers, (b), your workplace culture is to remove jackets, (c), those who may make decisions that can affect your career are not around, (d), your motivation is the same, jacket or no jacket, (e), you can get away with the lower level of motivation that comes with taking off your jacket, (f), all or more than one of the above, than take it off.
I can hear someone coming back from lunch and so I will end now, put my jacket back on, and at least look serious.