  We present radial velocities of the double-lined spectroscopic binary NP Aqr.
The radial velocities and the optical light curves obtained by Hipparcos and
ASAS-3 are analyzed separately. The masses of the primary and secondary
components have been found to be 1.65$\pm$0.09 and 0.99$\pm$0.05 M$_{\odot}$,
respectively. The cross-correlation functions indicate triple peaks which show
presence of a tertiary star. The spectroscopic properties of this additional
component resemble to that of the primary star. The analysis of the light
curves yielded that the more massive primary star fills its corresponding Roche
lobe. The secondary component is at or near Roche lobe indicating a new $\beta$
Lyrae-type near-contact binary. The orbital inclination is about 40$^{\circ}$
and, therefore, the observed light variations are produced only by the
proximity effects. Due to the absence of eclipses, the effective temperature of
the secondary star and the radii of the components could not be determined
accurately. We conclude that NP Aqr is a non-eclipsing double-lined
spectroscopic binary with a distance of about 134$\pm$7 pc. The absolute
parameters of the components are also compared with the evolutionary models.
While the location of the primary star seems to be suitable with respect to its
mass in the Hertzsprung-Russell diagram, the secondary component is located as
if a star having a mass less than 0.6 M$_{\odot}$. This discrepancy is
originated from very low effective temperature determined only from the light
curve produced by proximity effects. The distance to the third star appears to
be very close to that of the close binary which indicates that it may be
dynamically bounded to the binary.
