Costa has scored eight goals in six Premier League games this season and played for the full 90 minutes in Chelsea's 1-0 win at Sporting Lisbon in Champions League Group G on Tuesday night.
That was despite Mourinho suggesting the £32million summer signing from Atletico Madrid is doing virtually nothing in training for fear of exacerbating his hamstring problems.
"If I played 90 minutes it's clear that I'm okay," Costa said in Spanish paper Marca.
"I am feeling better all the time, and it is the boss' (Vicente del Bosque's) decision.
"During the week I have been working intensively with the physios because I have had some discomfort for a while."
Mourinho suggested Costa should be omitted from Spain's squad for the matches with Slovakia and Luxembourg this month, but insisted he would not contact Del Bosque to make the plea.
Costa does not expect Mourinho and Del Bosque to fall out over the issue.
"I do not think it's a thing that can happen," Costa added.
Source : PA