The 6502 has a patent on decimal addition (#3,991,307), but that's long-expired. MOS Technology got sued by Motorola for making the 6501/6502 because they viola

The 6502 has a patent on decimal addition (#3,991,307), but that's long-expired. MOS Technology got sued by Motorola for making the 6501/6502 because they violated Motorola's patents on the 6800 and took trade secret documents. IC masks are protected as of 1984 (mask work is essentially copyright for the die), but the 6502 predates that. Some companies (such as Intel) copyright the assembly-language mnemonics, but that wouldn't be an issue. I can't think of other issues with the 6502 but I'm not a lawyer. Note the MOnSter 6502, a copy of the 6502 built from discrete transistors. I should also point out Ben Eater's 8-bit CPU is a simple design, not a 6502.