The suspect is currently in police custody, being questioned by Metropolitan Police Service Counter Terrorism Command.
The stabbing took place just steps away from the site of Wednesday's bloody murder. The suspect is still at large.
Three men in their 20s were arrested by British police Saturday following the brutal fatal stabbing of a soldier earlier this week.
The English Defense League protested the "Islamification" of London while Newcastle Unites protested the English Defense League.
One man, identified as Michael Adebolajo, was reportedly known to a banned Islamist organization.