I have Arduino Pro Mini, HC-06 bluetooth module, and Mifare RC522 RFID reader. Bluetooth module connects to serial port, and RFID connects to SDA, SCK, MOSI, MISO, ground, reset, and 3.3V pins. I want to know if there might be a conflict between RFID reader and ATmega serial port. The reader will be used for reading and wiring cards. Bluetooth is there for monitoring.
The ATmega168 has separate pins for I2C (PC4:5), SPI (PB2:5), and UART (PD0:1). There will be no conflict between the devices provided you use the MFRC522 via either SPI or I2C. Note that the Arduino Pro Mini is programmed via its UART, so you may need to disconnect the HC-06 when programming via the serial port.