The Spain international has shaken off a hamstring problem and will play in Saturday's La Liga title decider at Camp Nou
The Spain international missed last weekend's 1-1 draw against Malaga due to a hamstring injury and he was doubtful for the match at Camp Nou.
However, Simeone has now made it clear that the prolific attacker is ready to play after resuming regular training action.
"Diego Costa is alright. He trained normally without any problems. He will start against Barcelona," the Argentine coach said at a press conference.
Atletico need just a point on Saturday to clinch the Spanish title, but Simeone is expecting Barca to come out firing as they look for the win which will see them retain their crown.
"I don't think that the game will be decided early on, but I expect Barcelona to start strong. I think we will see the best Barcelona of recent weeks," he warned.
"They have an extraordinary team and play at home. It will be one of the most complicated Barcelona teams we could possibly deal with.
"But we know what to expect. We know where our strengths lie and what our weaknesses are. We have to put in a great performance."
Barcelona coach Gerardo Martino is reportedly ready to alter his system for the game against Atletico, having failed to win any of the previous five meetings this season, but Simeone has stressed the Vicente Calderon side must be at their best regardless of Barca's tactics.
"I believe that Barcelona are always a dangerous team irrespective of their tactical plans and which players they field. They have several variants and are a team that's used to attacking," he added.
"All we can do is give our all and put in a great game."