The Atletico striker has enjoyed an outstanding season, scoring 34 goals in 45 appearances in all competitions.
His form has helped Atleti to the top of La Liga, while they have also reached the UEFA Champions League semi-finals, where they will face Chelsea.
Chelsea manager Jose Mourinho has made no secret of his desire to improve his strikeforce and Costa - currently one of the hottest properties in Europe - has been linked with a switch to Stamford Bridge.
Simeone says the rumours are simply "normal", though.
"His future depends on him and what he feels is best for his future," he told AS.
"It's normal that Chelsea are interested in him.
"They are an economic power, Samuel Eto'o is getting older and Costa can do his work, but right now he's ours."
Simeone added that Costa's recent knee injury - sustained when he crashed into the post after scoring in Atletico's 2-0 win at Getafe - was "not worrying" him.
Costa left the field on a stretcher but will be hopeful of featuring in Friday's La Liga fixture against Elche.
