The 26-year-old's friends are concerned that she is planning to reconcile with the "Yeah 3x" hitmaker, even though she initially snubbed his messages.
"Chris started texting Rihanna on her birthday Feb 20, and the two have been sending each other a flurry of texts ever since," a source told the New York Post newspaper.
"Rihanna didn't write back right away...but later that night she started getting sentimental and texted back, 'Thank you,' and asked how he was. Since then, the two haven't stopped texting each other and friends are freaked out that she's going to start dating him again," the source added.
Brown, who recently underwent a 90-day rehabilitation programme for anger management, first split from Rihanna in 2009 after he violently assaulted her. But later they had an on-and-off relationship after her restraining order against him expired two years later.