The company, Typo Products LLC, is currently taking pre-orders for the $99 keyboard, which features angled miniature keys similar to those used on many of BlackBerry's devices.
Canada's BlackBerry, a once dominant smartphone maker that has lost market share to the iPhone and other touchscreen devices, said Typo's keyboard infringes its own design.
The allegation has not been proven in court. Typo and Seacrest could not immediately be reached to comment on the legal proceedings.
"We are flattered by the desire to graft our keyboard onto other smartphones, but we will not tolerate such activity without fair compensation for using our intellectual property and our technological innovations," Steve Zipperstein, BlackBerry's chief legal officer, said in a statement.
BlackBerry posted billions in losses in recent quarters as its latest devices sold poorly, but it has maintained a loyal niche of customers who prefer to type on a physical keyboard.
The BlackBerry complaint is case no. 3:14-cv-23 in the United States District Court for the northern district of California.