How To Set Cursor Position In Textbox

In my application which is written on vb.net,i search for a word by typing the same in textbox here i have doubt to focus the cursor in the text box.. if i press first letter, say 'a', in textbox that will automatically search what are the words start with 'a'but after searching, cursor is not focussed in the textbox and to type another letter, say 'b', i need to bring my mouse pointer over the textbox and click so that i can type another letter.how can i keep my cursor focussed in the textbox unless i click somewhere else.