Cursor Focus on Textbox in WPF/C#

I am currently in the process of creating a Onscreen keyboard. I am handling the button click using routedcommands. The issue is that when i click on the button in keyboard panel the focus shifts to the button rather than on the Textbox. The requirement states that a cursor should always appear in the text box to indicate the position where the next character will be inserted. Is there a way i can keep focus on the textbox while button is clicked.