show message box on cross thread with owner

I want to show MessageBox on cross thread with providing owner object.like this :

if (MessageBox.Show(mainform,"message", "title", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button1) == DialogResult.Cancel)
                    {
                        return true;
                    }

by this code I am getting exception :

Cross-thread operation not valid: Control 'MainForm' accessed from a thread other than the thread it was created on.

I tied with checking InvokeRequired of mainform but still it's throwing same exception.