Ubuntu update error: Unable to lock directory /var/lib/apt/lists/

When I update using

sudo apt-get update
or
sudo apt update

I get following error.

E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)
E: Unable to lock directory /var/lib/apt/lists/

I tried updating through Software Updater and Restarted the machine.

Now its fine.