invalid combination of opcode and oeprands being thrown

Question

tst.asm:10: error: invalid combination of opcode and operands

  section .data
  biyt db 4
  
  section .bss
  
  section .text
  global _start
  _start:
      mov al, 16
      mov biyt, al
      
      call _exit
  
  _exit:
      mov rax, 60
      mov rdi, 1
      syscall

I'm using nasm elf64

nasm -f elf64 -o obj.o tst.asm

is my assemble command