Check if a specific tab page is selected (active)

Assuming you are looking out in Winform, there is a SelectedIndexChanged event for the tab

Now in it you could check for your specific tab and proceed with the logic

private void tab1_SelectedIndexChanged(object sender, EventArgs e)
{
     if (tab1.SelectedTab == tab1.TabPages["tabname"])//your specific tabname
     {
         // your stuff
     }
}

To check if a specific tab page is the currently selected page of a tab control is easy; just use the SelectedTab property of the tab control:

if (tabControl1.SelectedTab == someTabPage)
{
// Do stuff here...
}

This is more useful if the code is executed based on some event other than the tab page being selected (in which case SelectedIndexChanged would be a better choice).

For example I have an application that uses a timer to regularly poll stuff over TCP/IP connection, but to avoid unnecessary TCP/IP traffic I only poll things that update GUI controls in the currently selected tab page.

in .Net 4 can use

if (tabControl1.Controls[5] == tabControl1.SelectedTab)
                MessageBox.Show("Tab 5 Is Selected");

OR

if ( tabpage5 == tabControl1.SelectedTab)
         MessageBox.Show("Tab 5 Is Selected");