Abe's Liberal Democratic Party and its coalition partner Komeito would take between 67 to 76 of the 121 seats - half the chamber - available in the election, up from 59 previously, NHK said.
NHK's projection, based on exit polling and other analysis, came immediately after polls closed at 8 pm local time.
The two parties control 77 seats in the other half of the upper house that was not contested Sunday, meaning that according to the projection they are set to expand their majority in the 242-seat body.
The LDP and the Komeito were widely expected to do well despite public opinion polls showing lukewarm support as public confidence in opposition parties was seen as even lower.