Going for interview after accepting offer, good/bad idea?

Hey all,

So just days before I accepted my current offer from Company A I applied for a job for Company B, and now I got an email from Company B stating that they want to do an interview. Company B seems to pay more and offers a bit more benefits than Company A, and it is similar job duties than what I will be starting from Company A. Should I attend the interview just for practice and see what happens. Is this ethical? What do you guys think?

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official