Pattinson, who ended his four-year relationship with Stewart in May following her 2012 fling with married director Rupert Sanders, has sparked rumours the pair have rekindled their romance, reported E! Online.
"Rob looked nervous on his way to visit Kristen. He was trying to be discreet so no one would see him," a photographer said.
The 27-year-old star was recently seen hanging out with friend Riley Keough, the granddaughter of the late Elvis Presley.