Do you mean that the on-screen keyboard won't disappear even if you press the on-screen keyboard 'retract' key at the bottom right hand side of the keyboard?
If so, try a restart. Power down the iPad completely - press and hold the Power switch until the slider control appears and then accept the offer to power down. Once the screen has gone completely blank, power it back up again by pressing and holding the Power key until the white Apple logo appears. The iPad will then power up and hopefully, when it's up and running, the problem will have disappeared. Apple recommend you do this at least once a week.
Tim