Stop post back on some validation

Hi,

I need to stop Postback when some custom validation happens.Also some custom validation happens for repeater control. Below is the code I have written:

<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" CausesValidation="true" PostBackUrl="~/Test.aspx" />

When I enter some wrong data in repeater control and click on Submit button custom validation happens due to postbackURL I mentioned it is posting back to Test.aspx page. But I want to stop that postback because when wrong data entered Page.IsValid  is coming as false then I have to stay on the same page it shouldn't postback. How can I achieve that?

In code behind:

protected void btnSubmit_Click(object sender, EventArgs e)
{

if (Page.IsValid)
{

    //Do everything and post back to Test.aspx

}else{

   // Stay on the same page and stop post back to Test.aspx

}

}

Below I tried:

btnSubmit.Attributes.Add("OnClientClick","return false;"); it doesn't work still its post backing to Test.aspx.

Thanks....