The 33-year-old missed the series against New Zealand as well as the ICC Champions Trophy with a bruised knee, but scored 177 runs in his comeback match for Surrey.
While many regard him as brash and ostentatious, Pietersen insists that he is far from that.
"I've got this reputation of being confident, yet I go and do all these psychology tests and I'm an introvert," Pietersen told BBC Sport.
"I'm very much an introverted person, I like my own company, my own family, I don't really go out much.
"I think the confidence has grown from what I've achieved on the cricket field but I'm not as confident as anybody thinks."
The first Ashes Test against Australia begins on July 10 at Trent Bridge.