The simple low-pass filter is shown in Figure below. The filter has a 20dB/decade roll-off after its corner frequency fc. Its low-pass frequency gain (f->0) is defined by R3/R1. This allows low-frequency gains other than unity to be obtained.  R2 should be chosen equal to the parallel combination of R1 and R3 to minimize error due to bias current.

1st order active lpf circuit schematic

LMV721/722 is recommended for the op-amp, but any high impedance and high gain op-amp is applicable. For single stage filter, 5% tolerance is adequate, but 1% resistors is recommended if the filter is used as  cascaded part of third or higher odd order filter. [Circuit's schematic diagram source: National Semiconductor's Application Notes]