The sign, clearly visible behind the presenter, read "no war, stop the war, don't believe the propaganda, they are lying to you here".
The woman has been named as Marina Ovsyannikova, an editor at the channel.
Russian TV news is tightly controlled by the Kremlin and only reflects the Russian version of events in Ukraine.
Ms Ovsyannikova is believed to be in police custody.
Her voice could be heard during the broadcast saying "no to war! Stop the war!", before the programme director cut early to a recorded news report.