That issue could very well be a faulty keyboard. I had a similar issue with my T410 about a month after I bought it. Lenovo replaced the keyboard and the issue went away permanently. Try booting into Dell Diagnostics
and running the automated and manual keyboard tests.
n_K's theory that your issue is the ribbon cable could be correct, but if you have not serviced the hardware recently it seems much more likely that the actual keyboard is your issue. Regardless, you could visually inspect the keyboard's ribbon cable for crimps. I have seen the keyboards of many Macbook and Macbook Pro apparently fail because of a faulty ribbon cable. (Apple notoriously crimped the keyboard's ribbon cable in the Macbook and Macbook Pro 5.x models, which caused most of them to fail after a couple years.) It's possible that your laptop has the same issue, but I would definitely Google a bit to see if it is a known issue with your model. If failure of the keyboard ribbon cable is not a common issue with your model, it is very unlikely that is your issue.