Do you use the regular checkbox of mendix? This is linked to an attribute and is checked when true and otherwise false. If you want the checkbox to not be checked when you open the page, you should initialize it to false.
Hope this helps!
Hello Malay Modi,
I think you are setting by default value of attribute(used for checkbox) to true in domain model, that you need to set to False then checkbox will be unchecked by default.
Hope this helps you.