Absolutely!    

You can invest in ISA's alogside your pension as they are completely separate. It's key to underdtand the tax rules surrounding each type of investment though when making any decisions.    

For example:    

With pensions you can contribute up to £60,000 / or 100% of your salary (whichever is lower) a year and get tax relief on it all, however there are different thresholds for ISA's.  

Risk warnings: The value of your  investments can go up and down. Tax treatment is dependent on individual circumstances and subject to change.