Here is the sample JavaScript code to demonstrate that how can we validate a checkbox list inside the aspx page. Just call function vldChkBoxlist() and it will validate your checkbox list.

function vldChkBoxlist()
{
var tableBody = document.getElementById(‘CheckBoxList1’).childNodes[0];
for (var i=0;i<tableBody.childNodes.length; i++)
{
var currentTd = tableBody.childNodes[i].childNodes[0];
var listControl = currentTd.childNodes[0];
if (listControl.checked =true)
{
listControl.checked = false;
}
return false;
}