The Grid's CheckBoxColumn doesn't support the TextAlign property, making it impossible to center the checkbox with just Grid markup, you have to resort to a workaround.

The TextAlign property in other columns causes style="text-align: center" to be added to the underlying table cell.  This would also work for the checkbox column.

See this test:

<table class="table">
    <tr>
        <td class="table-active" style="width: 40px; text-align: center"><input type="checkbox" /> </td>
        <td>test</td>
    </tr>
</table>

Please add the TextAlign property to the CheckboxColumn.